DEFT* 


ITS  PROPERTIES,  ANALYSIS,  CLASSIFI 

CATION,  GEOLOGY,  EXTRACTION, 

USES  AND  DISTRIBUTION 


BY 

ELWOOD  S.  MOORE,  M.A.,  PH.D. 

PROFESSOR  OF  GEOLOGY  AND  MINERALOGY  AND  DEAN 
OF  THE  SCHOOL  OF  MINES  OF  THE  PENN- 
SYLVANIA STATE  COLLEGE. 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:  CHAPMAN  &  HALL,  LIMITED 

IQ22 


COPYRIGHT,  1922, 

BY 
ELWOOD  S.  MOORE 


TECHNICAL  COMPOSITION  CO. 
CAMBRIDGE,  MASS.,  U.  S.  A. 


PREFACE 


This  work  has  been  prepared  in  an  attempt  to  satisfy  the  demand 
for  a  handy  volume  on  coal.  There  already  exists  a  very  valuable 
literature  on  this  important  subject,  but  it  is  so  voluminous  and 
scattered  that  much  of  it  is  not  accessible  to  the  average  reader.  Many 
of  our  older  works  need  revision  because  of  new  discoveries  in  the 
study  of  coal,  such,  for  example,  as  the  practical  application  of  the 
microscope  in  the  determination  of  its  physical  character  and  the 
discovery  of  more  refined  chemical  processes  for  determining  its 
chemical  properties.  The  great  advances  in  extracting  coal  from  the 
earth  by  mechanical  means  and  in  the  cleaning  and  coking  of  the 
products  of  the  mine  also  make  it  necessary  to  bring  new  processes 
to  the  attention  of  the  public. 

There  are  so  many  different  phases  in  the  discussion  of  a  subject 
so  broad  as  this  that  details  regarding  many  matters  must  be  omit- 
ted in  a  one-volume  work,  and  readers  desiring  detailed  descriptions 
of  machines  or  complicated  processes  must  consult  works  dealing 
with  those  matters  alone.  While  many  topics  are  fully  dealt  with 
in  this  text,  such  as  the  properties,  the  origin,  the  uses  and  the  gen- 
eral distribution  of  coal,  some  others  as  mining  machinery,  and  de- 
tails of  distribution  and  character  of  local  coal  deposits  can  be  treated 
only  in  works  of  several  volumes.  It  is  hoped,  however,  that  the 
data  presented  will  serve,  for  ready  reference,  those  who  make  fre- 
quent use  of  a  work  of  this  type. 

I  wish  to  take  this  opportunity  of  expressing  my  appreciation  to 
those  who  have  so  generously  contributed  to  this  work.  My  thanks 
are  specially  due  to  Dr.  H.  Ries  of  Cornell  University,  at  whose  sug- 
gestion the  preparation  of  this  text  was  undertaken,  for  suggestions 
and  the  use  of  photographs  and  cuts.  I  am  also  particularly  obli- 
gated to  my  friend,  Professor  A.  Lacroix,  Secretaire  perpetuel  de 
1' Academic  des  Sciences,  Paris,  for  many  favors,  such  as  access  to  the 
library  of  the  Academy  and  to  valuable  collections,  including  Ren- 

iii 

469107 


IV  PREFACE 

ault's  slides  on  which  he  made  his  original  study  of  bacteria  in  coal. 
The  late  Dr.  Charles  R.  Zeiller  kindly  placed  at  my  disposal  his  works 
on  plant  fossils  and  the  coal  basins  of  France,  and  Monsieur  Peyerim- 
hoff  de  Fontenelle,  President,  le  Comite  Central  des  Houilleres  de 
France  generously  presented  me  with  a  copy  of  the  splendid  work, 
Atlas  General  des  Houilleres,  by  E.  Gruner  and  G.  Bousquet.  Dr. 
Aubrey  Strahan,  Director  of  the  Geological  Survey  of  England  and 
Wales  kindly  supplied  an  advance  copy  of  one  of  his  works  in  addition 
to  other  original  data.  My  thanks  are  due  also  to  Dr.  D.  F.  Mc- 
Farland,  and  to  Dr.  J.  B.  Hill  of  the  Pennsylvania  State  College, 
for  criticism  of  the  chapters  dealing  with  the  chemistry  of  coal  and 
with  paleobotany;  to  Professor  A.  L.  Kocher  for  retouching  photo- 
graphs, and  to  several  of  my  students  who  aided  greatly  in  copying 
diagrams,  sections  and  other  material. 

Although  acknowledgment  has  been  made  in  the  text  to  those 
from  whom  photographs  and  plans  have  been  received,  I  wish  to 
mention  particularly  the  officials  of  the  Twelfth  International  Geol- 
ogical Congress,  Dr.  F.  D.  Adams,  President,  who  kindly  granted 
me  permission  to  republish  the  various  maps  in  the  report  on  the 
Coal  Resources  of  the  World.  I  am  also  indebted  to  Coal  Age,  the 
Barrett  Company,  the  Delaware  and  Hudson  Company,  the  Koppers 
Company  and  the  Semet-Solvay  Company  for  the  privilege  of  re- 
producing illustrations.  Photographs  or  drawings  were  generously 
contributed  by  Dr.  R.  Thiessen  of  the  United  States  Bureau  of  Mines, 
the  Director  of  the  United  States  Geological  Survey,  Dr.  E.  C.  Jeffrey 
of  Harvard  University,  Dr  W.  R.  Crane,  Mr.  Francis  Harper,  the 
Hillman  Coal  Company,  the  Sullivan  Machinery  Company,  the 
Bethlehem  Fabricators,  the  Ebensburg  Coal  Company  and  Mr.  John 
Bevan  of  Pottsville,  Pa.  In  addition  to  those  persons  and  organiza- 
tions specifically  mentioned,  there  are  many  of  my  friends  and  col- 
leagues who  have  furnished  information  which  has  been  very  helpful, 
and  their  interest  and  aid  have  been  much  appreciated. 


ELWOOD  S.  MOORE 


STATE  COLLEGE,  PA. 
October  27,  1921. 


CONTENTS 

CHAPTER  PAGE 

I.  THE  PHYSICAL  PROPERTIES  OF  COAL i 

II.  THE  CHEMICAL  PROPERTIES  OF  COAL 18 

III.  CHEMICAL  ANALYSIS  OF  COAL 40 

IV.  VARIETIES  AND  RANKS  OF  COAL 82 

V.  THE  CLASSIFICATION  OF  COALS 105 

VI.  THE  ORIGIN  OF  COAL 123 

VII.  FOSSIL  FLORA  OF  THE  COAL-FORMING  PERIODS 178 

VIII.   STRUCTURAL  FEATURES  OF  COAL  SEAMS 214 

IX.  PROSPECTING  FOR  COAL  AND  THE  VALUATION  OF  COAL  LANDS 238 

X.  MINING  OF  COAL 264 

XI.  THE  PREPARATION  AND  USES  OF  COAL 299 

XII.  THE  GEOLOGIC  AND  GEOGRAPHIC  DISTRIBUTION  OF  COAL 328 

XIII.  THE  COAL  FIELDS  OF  THE  WORLD  —  AMERICA 336 

XIV.  THE  COAL  FIELDS  OF  THE  WORLD  —  EUROPE  AND  ASIA 407 

XV.  THE  COAL  FIELDS  OF  THE  WORLD  —  AFRICA  AND  OCEANIA 438 


COAL 


CHAPTER  I 
THE  PHYSICAL  PROPERTIES   OF  COAL 

Introduction 

History.  —  The  first  mention  of  coal  in  literature  dates  from  the 
fourth  century,  B.  C.,  but  so  rapidly  has  its  use  developed  that  it 
has  become  one  of  the  most  important  among  all  commercial  factors. 
The  enormous  production  of  approximately  1,478,000,000  short  tons1 
for  the  year  1913,  the  last  year  of  normal  production  before  the  great 
war,  indicates  how  useful  a  commodity  it  is  to  the  world.  This 
output  reckoned  at  the  average  price  of  the  coal,  as  sold  at  the  mine 
throughout  the  United  States  for  the  same  year,  would  reach  the  sum 
of  $1,965,740,000,  while  if  it  were  computed  at  the  price  prevailing 
in  England  or  France  it  would  be  from  nearly  two  to  two  and  one- 
half  times  this  amount.  Scarcely  any  home  or  industrial  concern 
among  white  races  can  exist  without  its  use,  directly  or  indirectly, 
although  as  recently  as  the  reign  of  Henry  II  of  France  it  was  con- 
sidered so  objectionable  a  fuel  that  the  smiths  in  Paris  obtained  a 
special  license  or  paid  a  fine  for  using  it.  There  were  regulations 
against  its  use  in  many  of  the  cities  of  Europe  during  the  seventeenth 
century  although  it  began  to  enter  actively  into  trade  in  England 
about  the  thirteenth  century.  Mining  did  not,  however,  become  very 
extensive  until  after  the  invention  of  the  steam  engine.  In  America 
the  first  bituminous  coal  mining  began  in  Virginia  in  1787  and  the 
first  recorded  shipments  of  anthracite  were  made  about  1805,  although 
anthracite  was  discovered  about  the  year  1762,  and  bituminous  coal 
in  1679.  The  earliest  records  of  production  of  bituminous  coal  in 
this  country  date  from  1820,  when  3000  tons  were  produced.  In 
1814  there  were  22  tons  of  anthracite  recorded.  The  million- ton 

1  Mineral  Resources,  U.  S.  Geol.  Survey,  1914,  Pt.  2,  p.  639. 

i 


PHYSICAL  PROPERTIES  OF  COAL 

mark  was  first  passed  for  anthracite  in  1837  and  for  bituminous  coal 
in  1850. 

History  shows  that  no  country  has  reached  an  eminent  industrial 
position  which  has  not  had  large  supplies  of  coal  within  its  borders 
or  had  ready  access  to  them.  Reference  to  the  prominent  nations  of 
the  present  day  proves  that  coal  and  iron  have  been  two  essential 
factors  in  their  development. 

It  has  been  said  that  the  Chinese  knew  the  use  of  coal  to  a  slight 
extent  before  the  Greeks  did,  but  the  first  definite  record  of  its  utiliza- 
tion is  found  in  Aristotle's  Meteorology.1  Speaking  of  the  combustible 
bodies  he  says,  "Those  bodies  which  have  more  of  earth  than  of  smoke 
are  called  coal-like  substances."  Theophrastus,  a  pupil  of  Aristotle, 
and  Pliny  both  mention  this  substance  and  its  use  by  the  smiths. 
The  coal  mentioned  in  these  writings  was  evidently  all  of  the  brown- 
coal  variety,  and  it  came  from  Thrace  in  northern  Greece  and  from 
Liguria  in  northwestern  Italy.  It  thus  became  known  to  the  ancients 
as  Thracius  lapis  and  gemma  Samothracia,  while  jet  which  came  from 
Lycia  in  Asia  Minor,  was  called  Gagates  after  a  river  in  that  region. 

The  word  coal,  as  now  used,  is  derived  from  the  Saxon  col.  It 
was  always  cole  in  English  until  sometime  in  the  seventeenth  century, 
and  coal  then  referred  to  charcoal  as  that  term  is  now  employed.  At 
the  present  time  the  term  coals  is  employed  in  two  senses,  one  meaning 
glowing  fragments  of  some  combustible  substance  and  the  other  the 
different  varieties  of  the  material  known  in  a  general  way  as  coal. 
The  Germans  use  for  coal  the  term  Steinkohle  and  the  French  speak  of 
it  as  charbon  or  charbon  de  terre. 

Coal  a  rock,  not  a  mineral.  —  Coal  is  the  term  applied  to  vegetal 
matter  with  varying  amounts  of  mineral  matter  and  with  or  without 
small  proportions  of  animal  matter,  which  through  geological  processes 
has  become  so  changed  by  loss  of  volatile  constituents  that  it  is  more 
or  less  compact  and  dark  in  color.  It  burns  with  comparative  slow- 
ness and  decomposes  slowly  in  the  atmosphere.  It  has  a  variable 
chemical  composition  and  it  is  not  homogeneous.  It  grades  into  peat, 
and  differs  from  that  substance  in  composition  chiefly  in  the  smaller 
percentages  of  water,  oxygen  and  volatile  hydrocarbons  which  it 
contains.  It  is  frequently  spoken  of  as  mineral  coal2  and  in  the 

1  Book  IV,  Chap.  9,  Sections  36-37.     (French  translation  by  B.  S.  Hilaire.) 

2  Dana,  E.  S.,  System  of  mineralogy,  6th  ed.,  1892,  p.  1021. 


INTRODUCTION  3 

United  States  coal  lands  are  classed  under  the  division  of  Mineral 
Lands.  It  is  not,  however,  a  mineral  in  the  strict  sense  of  the  term 
because  a  mineral,  as  denned  by  Dana,1  must  be  inorganic,  homoge- 
neous, and  have  a  definite  chemical  composition,  all  three  of  which 
requirements  coal  lacks.  Yet  it  might  be  questioned  whether  the 
varying  amount  of  impurity  in  the  form  of  ash  in  the  coal  is  not 
somewhat  analogous  to  the  impurities  which  are  present  in  some 
minerals  producing  coloring  effects  and  variation  in  other  physical 
properties,  and  also  whether  the  chemical  formulae  for  some  of  the 
complex  silicates,  such  as  members  of  the  amphibole  group,  do  not 
vary  almost  as  much  as  those  for  some  varieties  of  coal  when  ash  and 
moisture  are  eliminated. 

Although  not  a  mineral,  coal  is  a  rock,  since  the  geologist  regards  as 
rocks  all  natural,  solid  substances,  organic  or  inorganic,  which  com- 
pose the  earth's  crust.  It  is  as  much  a  rock  as  are  sandstone  and 
limestone,  and  when  one  attempts  to  classify  the  different  varieties 
of  coal  he  meets  with  the  same  difficulties  experienced  in  classifying 
other  rocks,  for  the  reason  that  Nature  does  not  draw  sharp  lines 
between  varieties.  It  is  just  as  difficult  to  decide  in  some  cases 
whether  a  certain  coal  is  bituminous  coal  or  anthracite  as  it  is  to 
determine  when  a  shale,  high  in  lime,  passes  into  a  limestone,  or  when 
an  igneous  rock  by  variation  ceases  to  be  a  syenite  and  becomes  a 
diorite.  As  a  result  of  this  lack  of  definiteness  in  the  delineation  of 
our  varieties  of  coal,  many  attempts  have  been  made  in  recent  years 
to  devise  some  concise  method  of  classifying  coals  so  that  all  the 
terms  employed  will  have  some  definite  meaning.  These  attempts 
have  met  with  some  of  the  same  difficulties  encountered  by  the  petro- 
graphers  who  have  attempted  the  quantitative  classification  of  ig- 
neous rocks.  Some  of  the  objections  are  that  in  many  cases  elaborate 
chemical  analyses  are  required,  and  in  most  cases  the  chemical  and 
physical  properties  and  the  field  characteristics  are  not  closely  enough 
related  to  make  the  classification  readily  applicable  to  all  varieties 
under  all  conditions. 

1  A  textbook  of  mineralogy,  p.  i. 


4  THE   PHYSICAL  PROPERTIES  OF   COAL 

Physical  Properties 

In  the  description  of  the  varieties  of  coal  certain  common  physical 
and  chemical  terms  much  used  in  mineralogy  are  employed.  The 
physical  properties  include  specific  gravity,  hardness,  fracture,  color, 
streak,  luster,  and  physical  constitution  or  texture.  These  are  the 
properties  by  which  the  public  recognizes  the  different  varieties  of 
coal  in  the  trade,  but  the  chemical  composition  is  the  determining 
factor  in  the  value  of  coal. 

Specific  gravity.  —  The  specific  gravity  of  a  body  is  the  ratio  of  its 
weight  to  the  weight  of  an  equal  volume  of  water  at  4°  C.  When  the 
average  specific  gravity  of  a  quantity  of  coal  is  known  the  space  which 
a  ton  will  occupy  can  be  roughly  determined,  it  being  always  remem- 
bered that  the  volume  of  a  ton  will  vary  with  the  size  to  which  the 
coal  is  broken.  The  gravity  of  the  common  varieties  of  coal  varies 
as  follows:  Lignite  0.5-1.30;  Bituminous  coal  1.15-1.5;  Cannel 
1.2-1.3;  Anthracite  1.29-1.65. 

There  are  various  methods  for  determining  the  specific  gravity  of 
coal.  It  may  be  determined  approximately  for  compact  fragments 
by  drying  the  specimen  carefully,  weighing  it  in  air  (weight  =  W), 
and  then  in  water  (weight  =  Wi).  Since  the  specimen  loses  in 
weight  an  amount  equal  to  the  weight  of  the  water  displaced,  i.e., 
the  weight  of  its  own  volume  of  water,  the  specific  gravity  is  found 

W 

from  the  following  formula:     G  =  — — .     Fora  more  accurate 

W  —  Wi 

determination  of  the  solid  substance  with  the  pores  omitted  the 
specimen  should  be  boiled  in  water  in  order  that  the  air  may  be  ex- 
pelled from  the  pores.  On  the  other  hand,  if  the  specific  gravity  of 
a  given  mass  of  coal  with  all  pores  included  is  desired  the  body  should 
be  coated  with  a  thin  veneer  of  paraffin  or  varnish  to  exclude  all 
water  from  the  pores. 

Determination  by  use  of  pycnometer:  Accurate  laboratory  deter- 
minations may  be  made  on  powdered  coal  by  using  the  pycnometer. 
This  is  a  glass  vessel  which  when  filled  to  a  specified  mark  contains 
a  given  weight  of  water  at  a  certain  temperature.  The  dry  powder 
is  weighed  in  air  (weight  =  W).  The  pycnometer  is  weighed  full 
of  water  (weight  =  Wi),  and  then  emptied.  The  powder  is  then 
placed  in  the  vessel,  all  air  is  excluded,  the  water  is  brought  to  the 


SPECIFIC   GRAVITY  5 

same  level  as  before  the  coal  was  added  and  the  vessel  is  weighed 
(weight  =  W2).     The  specific  gravity  is  then  obtained  from  the  fol- 

W 

lowing  formula  G  =  w  +  Wi  _  w; 

The  following  methods  for  determining  the  specific  gravity  of  coal 
and  coke  are  used  in  the  fuel-testing  laboratories  of  the  United  States 
Bureau  of  Mines.1  To  determine  the  true  specific  gravity  the  pyc- 
nometer  is  ordinarily  employed  and  about  3.5  grams  of  the  6o-mesh 
coal  or  coke  is  used  as  a  sample.  About  30  c.c.  of  distilled  water  is 
employed  in  a  5o-c.c.  pycnometer,  and  the  water  is  thoroughly  boiled 
after  the  sample  is  placed  in  the  bottle,  for  the  purpose  of  excluding 
all  air.  The  boiling  is  done  on  a  water-bath  and  to  avoid  loss  of  par- 
ticles of  the  coal  or  coke  a  one-bulb,  6-inch  drying  tube  is  connected 
with  the  pycnometer  by  means  of  a  small  piece  of  pure  gum  tubing. 
This  drying  tube  is  then  attached  to  an  aspirator  and  suction  is 
applied  while  the  water  in  the  flask  is  gently  boiled  for  three  hours. 
The  tube  is  then  detached,  the  flask  removed  from  the  bath,  and 
almost  filled  with  water  previously  boiled  and  cooled.  When  cooled 
to  the  temperature  of  the  room  at  which  original  weighing  was  made, 
the  pycnometer  is  stoppered  and  weighed.  The  formula  employed 

W 

is  the  same  as  that  given  above,  G  =  _    — . 

Determination  by  Hogarth-flask:  A  special  method  is  recommended 
as  being  more  convenient  and  accurate  for  routine  determinations 
than  the  pycnometer  method.  This  consists  in  the 
use  of  a  Hogarth  flask  such  as  that  used  in  deter- 
mining the  specific  gravity  of  iron  ores.  (Fig.  i.) 
This  flask  has  a  capacity  of  100  to  125  c.c.  To 
make  the  test  a  lo-gram  sample  of  6o-mesh  coal 
or  coke  is  weighed  and  introduced  into  the  weighed 
flask  together  with  sufficient  distilled  water  to  fill  it 
half  full.  The  flask  is  placed  on  a  small  electric 
hot  plate  inside  a  lo-inch  vacuum  desiccator  and 
the  latter  is  evacuated  by  an  aspirator  or  air  pump.  IG*  It  ?gar*  f 

r     specific  gravity  flask. 

The  water  in  the  flask  is  kept  boiling  and  the  air 

is  expelled  in  thirty  minutes  with  a  good  air  pump.     The  flask  is 

then  removed  from  the  desiccator  and  filled  to  the  tubulure  with 

1  Stanton,  F.  M.,  and  Fieldner,  A.  C.,  Tech.  Paper  8,  1913. 


6  THE   PHYSICAL  PROPERTIES  OF   COAL 

distilled  water  which  has  recently  been  boiled  and  cooled.  The 
stopper  is  inserted  after  having  been  coated  with  a  thin  film  of  vaseline 
to  prevent  leakage. 

After  the  flask  has  cooled  to  about  25°  C.  in  a  water  thermostat, 
distilled  water  that  has  been  cooled  in  the  same  thermostat  is  drawn 
through  the  tubulure  until  the  water  level  is  slightly  above  the  mark 
on  the  capillary  of  the  stopper.  If  the  end  of  the  tubulure  be  inserted 
in  a  small  beaker  of  water  and  a  slight  suction  applied  to  the  stopper 
this  operation  may  be  performed  without  removing  the  flask  from  the 
thermostat.  The  flask  should  be  left  in  the  thermostat  until  the 
temperature  is  25°  C.  The  water  level  may  be  adjusted  to  the  mark 
in  the  capillary  by  drawing  in  a  little  water.  When  this  is  done  the 
flask  is  removed,  wiped  dry,  and  weighed.  The  true  specific  grav- 
ity is  then-  found  by  the  formula  used  in  the  previously  described 
test. 

Hydrometer  method:  To  determine  the  apparent  specific  gravity 
an  apparatus  is  used  which  consists  of  a  brass  hydrometer  immersed 
in  a  galvanized-iron  cylinder  filled  with  water  to  a  water-line.  There 
are  two  pans  on  the  top  of  the  hydrometer,  the  upper  one  being  used 
for  weights  and  the  lower  for  the  sample  of  coal  or  coke.  Below  the 
copper  air  buoy  there  is  a  brass  cage  highly  perforated  so  as  to  allow 
the  air  to  escape  during  immersion.  This  cage  carries  the  sample 
when  it  is  weighed  under  water. 

To  determine  the  specific  gravity  with  this  apparatus,  brass  weights 
are  placed  on  the  upper  pan  causing  the  hydrometer  to  sink  to  a  mark 
on  the  stem  between  the  pan  and  the  buoy.  This  weight  is  desig- 
nated by  (W).  The  weights  are  removed  and  about  500  grams  of 
the  sample  in  ij  to  2  inch  cubical  lumps  is  placed  in  the  copper  dish. 
Weights  are  again  added  until  the  instrument  sinks  to  the  same 
mark  on  the  stem  as  it  did  previously,  (weight  =  Wi).  The  sample 
is  then  transferred  to  the  perforated  cage  and  weights  are  added  until 
the  same  mark  on  the  stem  again  touches  the  surface  of  the  water; 
(weight  =  W2).  We  now  have  the  following,  (W  —  Wi)  =  weight 
of  sample  in  air,  and  (W  —  W2)  =  weight  of  sample  in  water.  Since 
the  body  loses  in  weight  when  weighed  in  water  an  amount  equal  to 
the  weight  of  the  water  displaced  the  apparent  specific  gravity  = 
W  -  Wt 

(w  -  wo  -  (w  -  w2y 


SPECIFIC   GRAVITY  7 

Further,  in  determining  the  specific  gravity  of  coke  100  X 
apparent  specific  gravity  =  ntage  by  volume  of  coke  substance, 

true  specific  gravity 

and   100  —  percentage  by  volume  of  coke  substance  =  percentage 
by  volume  of  cell  space. 

Certain  precautions  are  observed  in  making  apparent  specific 
gravity  tests  on  coke.  It  should  preferably  be  in  lumps  of  nearly 
the  same  size  and  shape,  and  when  the  sample  is  immersed  the  hy- 
drometer should  be  moved  rapidly  up  and  down  a  few  times  to  remove 
air  bubbles.  Coke  samples,  because  of  their  marked  porosity,  should 
not  remain  in  the  water  more  than  five  minutes  and  all  specimens  of 
coal  or  coke  should  be  thoroughly  dried  before  tests  are  made. 

Use  of  heavy  solutions  in  determination  of  specific  gravity:  In  an 
investigation  of  the  Canadian  coals  Porter  and  Durley1  used  a  heavy 
solution  consisting  of  calcium  chloride  and  calcium  nitrate  mixed  so 
as  to  obtain  required  densities.  The  crushed  coal  was  placed  in  this 
solution  and  separated,  the  heavier  sinking,  the  lighter  rising  to  the 
top,  and  that  of  the  same  gravity  as  the  solution  floating  suspended 
in  the  liquid. 

Gravity  of  "ash-free"  and  "moisture-free"  specimens:  In  case  it 
is  desired  to  obtain  the  specific  gravity  of  the  pure  fuel  with  moisture 
and  ash  excluded  a  correction  must  be  made  for  these.  The  actual 
specific  gravity  of  the  ash  may  be  obtained,  or,  as  Pollard2  suggests, 
the  correction  for  ash  may  be  made  with  a  sufficient  degree  of  accuracy 
for  all  practical  purposes  by  deducting  o.oi  from  the  specific  gravity 
of  the  coal  for  each  per  cent  ash. 

As  a  rule,  high-carbon  coals  have  higher  specific  gravities  than 
those  low  in  carbon  because  of  their  more  compact  character.  It 
might  be  expected  that  the  percentage  of  ash  would  be  the  factor 
controlling  the  specific  gravity  of  the  coal  in  all  cases  since  the  mineral 
matter  entering  the  ash  has,  as  a  rule,  a  higher  specific  gravity  than 
the  materials  forming  the  combustible  portion  of  the  fuel,  and  this  is 
generally  true  if  the  proportions  of  the  other  constituents  remain 

1  Porter,  J.  B.,  and  Durley,  R.  J.,  An  investigation  of  the  coals  of  Canada.    Canada 
Dept.  of  Mines,  Vol.  i,  pp.  194  and  199,  1912. 

2  Strahan,  A.,  and  Pollard,  W.,  The  Coals  of  South  Wales  with  special  reference  to  the 
origin  and  distribution  of  anthracite.    Memoirs  of  the  Geol.  Survey  of  England  and 
Wales,  2d  ed.,  p.  12,  1915. 


8  THE   PHYSICAL  PROPERTIES  OF  COAL 

constant.  It  is  found,  however,  from  a  study  of  a  large  number  of 
analyses  that  there  is  no  regular  ratio  between  the  percentage  of  ash 
and  the  specific  gravity,  and  this  seems  to  be  due  to  a  variation  in 
the  volatile  constituents,  and  the  compactness  of  the  fuel.  It  de- 
pends also  upon  the  nature  of  the  ash  since  the  presence  of  iron  com- 
pounds tends  to  raise  the  specific  gravity  above  that  for  silica,  alumina 
and  many  other  constituents. 

That  the  specific  gravity  has  a  direct  bearing  on  the  burning  qual- 
ities of  the  coal  is  seen  in  the  statement  of  Porter  and  Durley,1  who 
conclude  as  a  result  of  their  investigation  of  Canadian  coals  that  few, 
if  any,  coals  which  have  a  specific  gravity  over  1.6  are  worth  burn- 
ing and  that,  excepting  the  anthracites  and  perhaps  one  or  two  special 
types  of  coals,  the  approximate  limit  for  commercially  profitable 
coals  is  1.55.  They  add  further  that  the  pure  bituminous  coals  of 
Canada  have  a  specific  gravity  between  1.265  and  I-325- 

Hardness.  —  The  hardness  of  coal  varies  from  that  of  the  soft 
lignites  to  that  of  the  hard  anthracites.  It  is  difficult  to  state  any 
definite  hardness  for  the  coals  other  than  anthracite  because  they 
vary  so  much  in  different  portions  of  the  same  fragment.  Anthracite 
varies  from  2  to  2.5  in  Moh's  scale  of  hardness,  which  means  that  it 
can  be  scratched  with  difficulty  by  the  finger  nail. 

Fracture.  —  The  fracture  in  coal  is  a  very  important  determining 
factor  in  recognizing  the  ordinary  types  in  hand  specimens.  The 
anthracites  break  with  a  conchoidal  fracture,  i.e.  the  fracture  leaves 
a  concave  surface  like  that  of  a  shell.  This  is  characteristic  also  of 
cannel  coal,  but  the  other  varieties  of  bituminous  coal  generally  break 
with  a  rectangular  or  cubical  fracture.  The  lignites  fracture  so  that, 
as  a  rule,  they  break  into  roughly  tabular  or  flat,  elongated  fragments. 
(Plates  III  and  IV.) 

In  coal  beds  there  are  usually  two  sets  of  joints  resulting  from  the 
drying  out  of  the  rocks  and  the  movement  of  the  strata  and  these 
run  approximately  normal  to  each  other.  Those  which  lie  normal  to 
the  strike  and  cut  across  the  bedding  of  the  coal  are  frequently  known 
as  cleats.  They  are,  as  a  rule,  more  clearly  marked  than  the  joints 
running  in  the  other  direction. 

Color  and  streak.  —  The  color  of  coal  varies  from  light  to  dark 
brown  in  the  lignites  to  grayish  black  and  jet  black  in  the  higher 

1  Op.  cit.,  p.  194. 


PHYSICAL  CONSTITUTION  9 

grades.  The  streak  is  the  color  of  the  powder  and  it  is  determined 
by  making  a  mark  on  a  piece  of  unglazed  porcelain.  For  the  coals 
below  bituminous  it  is  brown  to  yellow.  In  bituminous  coal  it  is 
brownish  to  black  and  in  cannel  it  is  brown  to  black.  The  streak  of 
the  higher-rank  coals  is  black. 

Luster.  —  The  luster,  or  the  manner  in  which  the  coal  reflects 
light  from  its  surface,  is,  like  the  fracture,  often  an  important  diag- 
nostic property  in  a  hand  specimen.  The  anthracites  have  usually 
a  bright  to  almost  submetallic  luster  and  the  luster  of  natural  coke  is 
bright  to  submetallic,  while  that  of  cannel  coal  is  usually,  and  that  of 
mineral  charcoal,  always,  dull  to  earthy.  Slaty  coal  is  dull.  In  bi- 
tuminous coal  there  are  interlayered  bright  and  dull  bands,  the  former 
representing  portions  of  the  coal  formed  from  trunks  or  branches  of 
trees,  and  the  latter  portions  being  made  up  of  mineral  charcoal 
and  the  smaller  particles  of  vegetal  matter  or  sometimes  of  impure 
earthy  layers. 

Physical  constitution.  —  That  coal  has  been  derived  almost  en- 
tirely from  vegetal  matter  is  proven  by  the  presence  in  lignite  of 
abundant  remains  of  plants  and  by  the  presence  in  decreasing  amounts 
of  distinctly  recognizable  plant  remains  in  all  the  varieties  of  coal 
from  lignite  to  anthracite.  While  some  anthracite  may  not  show  a 
trace  of  woody  tissue  to  the  naked  eye,  or  even  under  the  microscope, 
some  other  portions  of  this  coal  from  the  same  seam  may  show  dis- 
tinct evidence  of  the  presence  of  vegetal  constituents  now  altered  to 
coal.  The  microscope  has  been  of  great  service  in  recent  years  in 
aiding  us  in  detecting  the  presence  of  altered  vegetal  remains  in  coals 
where  they  were  not  formerly  recognized  by  the  naked  eye.  The 
effects  of  the  different  kinds  of  vegetation  or  the  different  portions  of 
the  same  types  of  vegetation  which  enter  into  the  coal  may  now  be 
recognized  through  the  varying  appearances  of  the  coal  produced 
from  these  different  materials.  It  is  found  that  the  spores  from  the 
Cryptogamic  plants  which  can  be  recognized  under  the  microscope, 
if  comparatively  free  from  other  materials  will  produce  the  dull- 
lustered  cannel  bands,  the  stems  of  trees  usually  produce  bright 
bands  in  the  coal,  while  resins  generally  produce  light-colored  spots 
or  streaks.  It  has  been  found,  therefore,  that  coal  is  usually  made 
up  of  the  following  constituents:  (a)  distinctly  woody  or  xyloid 
material,  so  abundant  in  lignite  and  to  which  Thiessen  has  given 


PLATE  I. 


FIG.  i.  Photomicrograph  of  coal  from  No.  6  seam,  Royalton,  111.  (x  160). 
Distinct  woody  tissue  and  a  few  flattened  spores  are  visible.  (After  R. 
Thiessen.) 


FIG.  2.     Same  as  Fig.  i.     Shows  little  xyloid  tissue  but  many  flattened 
spores  as  white  lines.  /Io) 


DEVELOPMENT   OF   THE   MICROSCOPIC   STUDY  II 

the  name  anthraxylon,  from  the  Greek  anthrax,  coal  and  xylon,  wood. 
(b)  canneloid,  consisting  chiefly  of  spores  and  forming  the  bulk  of 
cannel  coal;  (c)  resins  found  in  all  coals  but  especially  evident  in 
lignite  and  scarce  in  cannel;  (d)  de"bris,  or  the  macerated  material 
mixed  with  the  woody  matter  and  derived  from  a  great  variety  of 
substances  by  the  breaking  up  of  stems,  cells,  cuticles,  spores,  and 
particles  of  resin;  (e)  the  " fundamental  matter,"1  or  the  colloidal 
groundmass  in  which  the  other  constituents  of  the  coal  are  embedded 
and  which  is  made  up  chiefly  of  the  remains  of  the  more  readily  de- 
composable parts  of  the  vegetal  matter.  It  seems  to  consist  chiefly 
of  fragments  of  cellulosic  material,  cuticles,  cutinized  cell  walls,  spore- 
exines,  pollen-exines,  fragments  of  wood  fiber,  bits  of  resin,  and  all 
the  other  finer  particles  of  the  material  entering  into  the  composition 
of  the  coal.  Some  authors  consider  that  large  quantities  of  algal 
remains  are  included  in  this  substance  and  this  subject  will  be  dis- 
cussed more  fully  in  the  chapter  on  the  origin  of  coal 

The   Microscopic   Study   of   Coal 

Development  of  the  microscopic  study.  —  The  subject  of  the 
physical  constitution  of  coal  has  received  a  great  deal  of  attention 
during  the  last  century  and  a  half,  and  the  historic  development  of 
this  study  is  well  treated  in  the  work  by  White  and  Thiessen.  As 
early  as  1778  Franz  von  Beroldingen2  outlined  a  logical  theory  for 
the  development  of  the  coal  swamps  and  for  the  origin  of  petroleum. 
In  1833  H.  Witham3  made  what  was  probably  the  first  microscopic 
examination  of  coal  and  his  work  was  followed  by  that  of  Hutton.4 
In  1838  Link5  boiled  coal  fragments  in  kerosene  to  render  them  more 
nearly  transparent  for  microscopic  study.  In  1855  Franz  Schulze6 

1  White,  D.,  and  Thiessen,  R.,  The  origin  of  coal.     U.  S.  Bur.  of  Mines,  Bull.  38,  p. 
227,  1913. 

2  Von  Beroldingen,   Franz,   Beobachtungen,  Zweifel,  und  Fragen,  die  Mineralogie 
iiberhaupt,  und  insbesondere  ein  natiirliches  Mineral  System  betreffend,  vol.  i,  ist  ed., 
1778,  2d  ed.,  1792. 

3  Witham,  Henry,  On  the  internal  structure  of  fossil  vegetables  found  in  the  carbon- 
iferous and  oolitic  deposits  of  Great  Britain,  1833. 

4  Hutton,  W.,  Observations  on  coal.     London  and  Edinburgh  Phil.  Mag.  and  Jour, 
of  Science,  vol.  2,  p.  302,  1833. 

5  Link,  Frederick,  Uber  den  Ursprung  der  Steinkohlen  und  Braunkohlen  nach  mikro- 
skopischen  untersuchungen.     Abhandl.  k.  Preuss.  Akad.  Wiss.  Berlin,  pp.  33-34,  1838. 

6  Schulze,  Franz,  Uber  das  Vorkommenwohlerhaltenes  Cellulose  in  Braunkohle  und 
Steinkohle;  Ber.  k.  Akad.  Wiss.  Berlin,  pp.  676-678,  1855. 


12  THE  PHYSICAL  PROPERTIES   OF  COAL 

adopted  the  maceration  process  for  lignite  and  bituminous  coal. 
He  digested  the  material  in  a  mixture  of  dilute  nitric  acid  and  potas- 
sium chlorate  and  then  washed  it  in  ammonium  hydroxide  and  hot 
alcohol,  thus  isolating  woody  fibers. 


FIG.  2.     Photomicrograph  of  bituminous  coal  showing  bright  bands  due  to 
woody  material  and  dark  bands  due  to  debris.     (Photo  by  Thiessen.) 

The  work  of  these  investigators  was  followed  by  that  of  J.  W. 
Dawson,  C.  W.  von  Giimbel,  C.  E.  Bertrand,  B.  Renault,  H.  Potonie, 
O.  Barsch,  D.  White,  and  E.  C.  Jeffrey,  all  of  whom  have  paid  par- 
ticular attention  to  the  microscopic  characters  of  coal.  It  was  not, 
however,  until  about  1910  that  a  satisfactory  method  was  found  for 
preparing  thin  sections  for  study.  This  was  discovered  by  Jeffrey 
and  described  in  his  article  published  in  that  year.1 

Preparation  of  thin  sections.  —  In  the  preparation  of  thin  sections 
with  the  microtome  there  are  two  chief  operations  necessary,  one  the 
removal  of  the  mineral  matter  and  the  other  the  softening  of  the  coal 

1  Jeffrey,  E.  C.,  The  nature  of  some  supposed  algal  coals.  Proc.  Am.  Acad.  of  Arts 
and  Sci.,  vol.  46,  pp.  273-290,  1910. 


PREPARATION  OF  THIN   SECTIONS  13 

so  that  it  may  be  cut  on  the  microtome  like  an  ordinary  botanical 
or  zoological  section.  The  chief  agent  used  for  the  removal  of  the 
mineral  matter,  which  consists  mainly  of  silica,  pyrite  and  carbon- 
ates3  is  hydrofluoric  acid  and  the  softening  agent  is  potassium  or 
sodium  hydroxide.  Jeffrey  has  recently  concluded,  however,  that 
phenol  is  a  still  better  softening  agent  since  it  does  not  cause  so  much 
swelling  of  the  coal.1  As  to  whether  the  hydroxide  should  have  water 
or  alcohol  added  to  it  or  be  employed  hot  or  cold  depends  upon  the 
resistance  of  the  coal  Thiessen2  points  out  that  alcohol,  by  causing 
shrinkage,  has  the  advantage  of  counteracting  the  expanding  influence 
of  the  hydroxide  but  it  causes  a  more  violent  reaction.  For  cannel 
Jeffrey3  used  a  mixture  of  yo-per  cent  alcohol  saturated  with  sodium 
or  potassium  hydroxide.  He  allowed  the  coal  to  stand  in  this  for 
a  week  or  more  at  a  temperature  of  60°  to  70°  C.  until  it  was  softened. 
The  mixture  was  then  carefully  removed  by  hot  alcohol  and  the  frag- 
ments later  treated  with  hydrofluoric  acid  for  two  or  three  weeks. 
After  this  treatment  the  acid  was  washed  out  very  thoroughly  so 
that  no  trace  of  it  might  attack  the  knife,  the  coal  was  embedded  in 
celloidin  to  stiffen  it,  and  was  then  cut  on  a  microtome.  The  celloidin 
recommended  is  that  known  as  Schering's.  For  those  coals  which 
are  more  resistant  to  the  softening  process  he  uses  either  aqua  regia 
(HNO3  +  3  HC1)  or  nitric  and  hydrofluoric  acid  of  full  strength. 
He  found  that  the  acid  treatment  in  many  cases  must  be  followed 
by  a  treatment  with  sodium  or  potassium  hydroxide  after  the  acid 
is  removed.  After  the  sections  are  cut  they  are  dehydrated  in  a 
mixture  of  absolute  alcohol  and  chloroform.  One  difficulty  was 
experienced  in  preparing  the  sections  for  cutting;  this  was  the  fact 
that  hot  alcohol  and  ether  must  be  used  in  embedding  the  specimens 
in  the  celloidin  and  these  solvents  dissolve  some  portions  of  the  lower 
grades  of  coal. 

After  various  experiments  Thiessen  recommends  that  mineral 
acids  such  as  nitric  acid,  be  avoided  if  possible,  owing  to  their  oxidiz- 
ing action  on  the  coal.  In  place  of  nitric  acid  alternate  applications 
of  hydrofluoric  acid  and  potassium  or  sodium  hydroxide  may  be  used 
to  soften  resistant  samples.  In  treating  the  samples  with  hydro- 

1  Jeffrey,  E.  C.,  Methods  of  studying  coal.     Conspectus,  Vol.  6,  No.  3,  1916. 

2  .Thiessen,  R.,  Op.  cit.,  p.  207 

3  Jeffrey,  E.  C.,  Op.  cit. 


THE   PHYSICAL  PROPERTIES  OF   COAL 


fluoric  acid  they  should  be  placed  in  paraffin,  ceresin,  or  rubber  bottles 
rather  than  in  lead.  For  lignite  a  good  solution  is  one  part  commer- 
cial hydrofluoric  acid  and  one  part  of  30  to  50  per  cent  alcohol  In 
which  the  blocks,  which  have  been  cut  about  2  to  4  millimeters  square 
and  10  millimeters  long,  are  placed  until  the  mineral  matter  is  dis- 
solved. The  acid  may  then  be  removed  by  potassium  hydroxide 
or  sodium  hydroxide  and  the  section  cut  on  the  microtome  without 

further  softening. 

If  the  specimens  are 
resistant  and  need  sof- 
tening a  5  per  cent  solu- 
tion of  sodium  hydroxide 
in  50  per  cent  alcohol  is 
used.  If  they  are  friable 
they  may  be  embedded 
in  paraffin  but  this  must 
not  be  allowed  to  actually 
penetrate  the  coal.  The 
sections  may  be  bleached 
in  nitric  acid  or  Javel 
water.  After  dehydra- 
tion they  may  be  mounted 
on  slides  with  Canada 
balsam. 

Thiessen  has,  in  his 
more  recent  work,  abandoned  the  use  of  the  microtome  and 
adopted  the  grinding  method  since  this  has  one  distinct  advantage 
over  the  slicing  method.1  By  preparing  the  specimens  in  this  way 
no  part  of  the  coal  or  its  included  foreign  matter  is  removed  by 
the  acids  or  other  reagents  and  all  the  features  of  the  coal  may 
be  studied.  It  has  a  disadvantage,  however,  in  that  several 
sections  cannot  be  cut  from  the  same  specimen  of  coal  almost  as 
easily  as  one.  When  the  coal  is  once  softened  it  is  an  easy  task  to 
cut  on  the  microtome  many  sections  from  the  same  block,  for  the 
study  of  the  internal  structure  of  bodies  occurring  in  the  coal.  The 
sections  of  anthracite  or  bituminous  coal  must  be  ground  extremely 

1  White  D.,  and  Thiessen  R.,  The  origin  of  coal.      Bull.  38,  U.  S.  Bur.  Mines.    Also 
Thiessen  R.,  Structure  in  paleozoic  bituminous  coals.     Bull.  117,  1920. 


FIG.  3.  Baxton  megaspores  from  coal,  with 
air  sacks  and  showing  tri-radiate  lines  (x  25). 
(After  R.  Thiessen.) 


PREPARATION  OF   THIN   SECTIONS  15 

thin  to  permit  any  light  to  pass  through  them  and  it  is  only  after 
considerable  practice  that  this  grinding  process  can  be  successfully 
carried  out. 

In  preparing  the  sections  a  block  less  than  an  inch  in  diameter  is 
cut  from  the  coal.  The  preliminary  grinding  is  done  with  a  paste 
of  carborundum  powder  on  a  fine  textured  carborundum  lap,  then 
on  the  lap  without  any  powder  but  with  a  stream  of  water  playing  on 
the  lap.  The  specimen  is  then  rubbed  on  a  hone  with  a  stream  of 
water  running  over  it  until  it  is  perfectly  smooth  and  flat  on  the 
polished  side.  After  this  operation  the  specimen  is  waterproofed 
to  prevent  water  entering  the  coal  and  causing  it  to  swell.  This 
process  consists  of  soaking  the  polished  surface,  first  heated  to  about 
105°  C.,  in  paraffin  heated  to  the  same  temperature.  This  requires 
only  a  few  minutes. 

After  waterproofing,  the  specimen  is  cemented  to  a  slide  with  a 
strong,  transparent  cement  consisting  of  3  parts  of  Canada  balsam  to 
2  parts  of  marine  glue  which  have  been  heated  together  in  a  drying 
oven  at  a  temperature  of  about  105°  C.  for  a  sufficiently  long  time  to 
make  a  quickly  setting,  strong,  but  not  brittle  cement.  This  cement 
is  warmed  until  it  is  completely  liquid  and  the  specimen,  wiped  free 
of  any  excess  paraffin,  is  placed  in  it  and  pressed  down  in  such  a  way 
as  to  exclude  all  air  bubbles. 

The  grinding  of  the  section  is  continued  by  first  grinding  the  speci- 
men down  as  far  as  possible  in  the  same  manner  as  the  first  grinding 
was  done  and  then  finishing  it  on  the  hone.  Considerable  care  must 
be  exercised  in  doing  the  fine  grinding,  especially  when  the  section 
becomes  very  thin,  to  avoid  breaking  it  up,  and  frequent  exami- 
nations should  be  made  with  the  microscope  to  test  its  condition. 
All  powder  must  be  removed  from  the  specimen  by  washing  before 
it  is  rubbed  on  the  hone.  If  the  section  is  to  be  studied  in  oblique 
illumination  the  dry  specimen  should  be  polished  on  a  dry  hone  by 
drawing  it  over  the  hone  in  one  direction  only. 

By  means  of  thin  sections  prepared  as  described  above  photo- 
micrographs may  be  made  with  a  magnification  of  2000  diameters. 
A  detailed  study  can  be  made  of  the  internal  structure  of  the  coal  and 
such  a  study  throws  a  great  deal  of  light  on  the  composition  and 
origin  of  coals.  Thiessen  has  made  use  of  this  in  a  very  practical 
way  in  the  study  of  the  occurrence  of  sulphur  in  coal  and  in  the  cor- 


PLATE  II. 


FIG.  i.  Photomicrograph  of  horizontal  section  of  coal  from  the 
Pittsburgh  seam  showing  numerous  spores  (x  800).  (Photo  by  R. 
Thiessen.) 


FIG.  2.  Photomicrograph  of  a  section  from  the  coal  in  the  Black 
Creek  seam  (x  800).  It  shows  flattened  spores  peculiar  to  this  seam. 
(Photo  by  R.  Thiessen.) 


(16) 


PREPARATION  OF  THIN  SECTIONS  17 

relation  of  coal  seams.  It  has  been  found  that  most  coal  seams  carry 
certain  plant  spores  which  are  characteristic  of  those  seams  and 
which  distinguish  them  from  other  seams,  just  as  animal  fossils  dis- 
tinguish one  formation  from  another  in  a  sedimentary  series  (Plate  II). 
While  certain  spores  may  be  common  to  several  seams  there  are 
usually  one  or  more  types  found  only  in  one  seam.  The  microscope 
has  also  been  of  the  greatest  service  in  determining  the  origin  and 
character  of  boghead  coals  and  oil  shales. 


CHAPTER  II 
THE  CHEMICAL  PROPERTIES   OF  COAL 

Introduction 

The  chemistry  of  coal  and  its  derivatives  is  a  subject  of  extreme 
complexity  and  of  very  comprehensive  range.  It  cannot  be  treated 
fully  in  a  text  of  this  sort  but  the  main  principles  of  the  subject  are 
here  set  forth. 

Since  coal  has  been  derived  chiefly  from  woody  constituents  it 
consists  mainly  of  the  elements  which  go  to  compose  wood,  but  it 
differs  from  wood  in  composition  inasmuch  as  certain  proportions 
of  those  elements  have  been  changed  during  the  fermentation  and 
metamorphic  processes  which  have  altered  the  wood  to  coal.  There 
have  been  additions  to  the  woody  matter  during  the  growth  of  the 
vegetation,  through  streams  and  winds  carrying  particles  of  mineral 
matter  into  the  coal  swamps.  Again,  after  the  woody  matter  has 
changed  to  peat  and  even  to  the  higher  grades  of  coal,  percolating 
meteoric  waters  or  hot  magmatic  waters,  the  latter  rising  in  regions 
where  igneous  rocks  occur,  may  add  a  quota  of  their  dissolved  salts 
to  the  coal  and  increase  the  ash  and  sulphur  content.  In  some 
regions  of  igneous  activity  a  great  variety  of  mineral  compounds, 
some  comparatively  rare,  have  been  found  in  the  coals.  Besides  the 
vegetal  and  mineral  matter  a  certain  amount  of  animal  matter  may 
have  been  imprisoned  in  the  coal  and  this  may  have  caused  a  variation 
in  some  constituents,  especially  in  the  nitrogen  and  phosphorous 
content.  Fish  remains  have  been  found  in  the  rocks  associated  with 
coal  seams  in  many  localities,  a  notable  example  being  that  of  the  coal 
basin  at  Commentry,  central  France.  Fish  remains  have  been 
found  also  in  some  seams  of  cannel  coal  in  England. 

Constituents  of  Vegetation 

Cellulose  and  lignocellulose.  —  The  chief  constituent  of  vegetation 
which  goes  to  form  coal  is  cellulose,  the  formula  of  which  is  (C6Hi0O6). 
Many  writers  have  discussed  the  derivation  of  coal  from  woody  ma- 
terials as  if  cellulose  were  practically  the  only  important  constituent 

18 


CELLULOSE   AND   LIGNOCELLULOSE  19 

of  the  vegetal  matter  but  Clarke1  considers  that  wood  consists  more 
nearly  of  equal  proportions  of  cellulose  and  lignocellulose  (Ci2Hi8O9). 
The  latter  is  known  also  as  lignone  and  lignin  and  its  composition  is 
similar  to  that  of  jute  fiber.  From  the  formulae  of  these  two  com- 
pounds their  percentage  composition  is  as  follows: 

Cellulose  Lignocellulose 

C  44 . 44  per  cent  C  47 . 06  per  cent 

H    6.18        "  H    5.89 

O49-38  O  47-05 

If  the  composition  of  these  substances  be  compared  with  that  of 
wood  it  is  seen  that  the  wood  runs  higher  in  carbon,  averages  about 


FIG.  4.  Photomicrograph  of  section  of  bituminous  coal  from  No. 
5  seam,  Vandalia,  Indiana  (x  160).  Consists  chiefly  of  particles  of 
resin.  (Photo  by  R.  Thiessen.) 

the  same  in  hydrogen,  and  is  considerably  lower  in  oxygen.  A  fair 
average  composition  for  wood  is  C;  49.50,  H;  6.25,  and  O;  44.00  per 
cent.  It  will  vary  somewhat  with  the  inclusion  or  exclusion  of  the 
oils,  waxes,  and  gums  because  they  are  much  higher  in  carbon  and 
hydrogen  and  lower  in  oxygen  than  cellulose  and  lignocellulose. 

1  Clarke,  F.  W.,  The  data  of  geochemistry.     U.  S.  Geol.  Survey,  Bull.  616,  3d  ed., 
p.  739,  1916. 


20  THE   CHEMICAL  PROPERTIES  OF  COAL 

Resins,  fats  and  oils.  —  According  to  Thiessen1  the  coniferous 
resins,  resinoles,  or  resinolic  acids  contain  C;  76.8  to  83.63,  H;  9.7  to 
12.9,  and  0;  o.o  to  ii.n  per  cent.  The  waxes  contain  C;  80.32  to 
81.6,  H;  13.07  to  14.1  and  O;  4.5  to  6.61  per  cent.  The  fats  and  oils 
are  composed  of  C;  74  to  78,  H;  10.26  to  13.36,  and  O;  9.43  to  15.71 
per  cent. 

Salts  of  organic  acids.  —  There  have  also  been  found  in  lignites 
salts  of  organic  acids  such  as  whewellite,  calcium  oxalate,  hum- 
bold  tine,  ferrous  oxalate,  and  mellite,  the  latter  a  salt  of  aluminum 
and  mellitic  acid.  Clarke2  considers  that  since  oxalic  acid  is  readily 
formed  from  cellulose,  and  calcium  oxalate  *is  insoluble  it  is  remark- 
able that  the  oxalate  is  not  more  common  in  coal. 

Humus  acids.  —  Humic  acid  occurs  abundantly  in  peat  and  to  a 
considerable  extent  in  lignite.  The  analyses  of  Borntrager3  show 
that  in  the  black  humus  varieties  of  some  German  peats  there  are 
12.50  to  30.00  per  cent  of  humus  acids  to  about  50  per  cent  of  fiber. 
In  the  brown  coal  at  Falkenau,  Bohemia,  Von  John4  has  found  native 
humic  acid  as  a  black  crumbling  coaly  mass.  It  is  soluble  in  ammonia 
and  sodium  carbonate,  and  hydrochloric  acid  precipitates  all  ot  the 
organic  material  from  solution.  The  percentage  composition  is 
C,  54.98;  H,  4.64;  O,  39.98;  and  ash,  0.40;  dried  at  100°.  The 
calculated  formula  is  C46H46O25  and  it  resembles  somewhat  a  sub- 
stance found  in  the  brown  coal  of  Bavaria.  The  "  paper  coals" 
of  Russia  also  contain  humic  acid  in  considerable  quantity. 

The  paraffin  series.  —  The  presence  of  at  least  one  of  the  lower 
gaseous  members  of  the  paraffin  series  in  coal  has  long  been  recog- 
nized because  methane  (CH4)  or  marsh  gas  is  a  well-known  gas  in 
mines.  Chamberlin5  has  also  found  ethane  (C2H6)  to  be  present  in 
much  smaller  quantities.  It  is  found  in  pulverizing  the  coal.  The 
presence  of  some  of  the  higher  members  of  the  series  as  liquids  and 
solids  has  been  pointed  out  by  Thiessen  who  mentions  the  compounds 
(CnHae),  (C24H5o),  and  (C26H54)  discovered  by  Krafft  in  brown  coal. 

1  White,  D.,  and  Thiessen,  R.,  The  origin  of  coal.    U.  S.  Geol.  Survey,  Bull.  38,  p.. 

293,  1913- 

2  Op.  cit.,  p.  741. 

3  Quoted  by  Clarke,  Op.  cit.,  p.  744. 

4  Von  John,  C.,  Verhandl.  K.  k.  Reichsanstalt,  p.  64,  Feb.  3,  1891. 

6  Chamberlin,  R.  T.,  Notes  on  explosive  mine  gases  and  dusts.  U.  S.  Bur.  of  Mines, 
Bull.  26,  1911. 


THE   PARAFFIN  SERIES  21 

Paraffins  with  formulae  (Ci0H22)  and  (C32HG6)  have  been  described 
by  Cohen  and  Finn1  as  occurring  in  the  roof  of  a  Yorkshire  coal  seam. 
Hall2  separated  the  oils  (CiiH24)  and  (Ci3H28)  from  material  taken 
from  the  roof  of  a  coal  seam  in  North  Staffordshire,  and  Bedson3 
found  paraffins  in  the  Whitehaven  Collieries,  whose  formulae  were 
believed  to  vary  from  (Ci3H28)  to  (CisH38).  It  is  probable  that 
members  of  the  paraffin  series  are.  much  more  common  in  coal  than 
they  were  formerly  believed  to  be  but  they  are  likely  to  be  over- 
looked and  not  separated  in  analyses.  Jones  and  Wheeler4  have 
found  solid  paraffins  apparently  existing  free  in  several  British  coals 
by  treating  the  extract  obtained  by  the  solvent  action  of  pyridine 
and  chloroform  with  pentane.  This  solution  yields  crystals  of  paraf- 
fin wax  melting  between  55°  and  59°  C.  and  similar  in  composition 
to  those  obtained  by  the  destructive  distillation  of  the  coal.  The 
wax  forms  about  o.io  per  cent  of  the  total  weight  of  the  coals  exam- 
ined but  it  may  not  be  present  in  all  coals.  It  is  the  opinion  of  these 
writers  that  the  paraffins  exist  as  alkyl  or  paraffinoid  groups  attached 
chemically  to  another  non-alkyl  group,  R.  H.  The  paraffin  would 
thus  be  in  a  so-called  "  bound"  condition  and  would  occur  as  a  com- 
ponent part  of  a  molecule  whose  general  formula  would  be  repre- 
sented by  RH  —  CnH2n+i  where  n  may  have  any  value  up  to  at  least 
32.  When  coal  is  decomposed  thermally  the  "free"  paraffins  are 
rapidly  distilled  from  the  " bound"  molecules  according  to  the  fol- 
lowing system: 

R  H.CnH2n+i  -»  R  +  CnH2n+2        or 
R  H.CRH2n+i  — >  R  ~h  CnH2n+2  H-  CniH2ni 

In  somewhat  the  same  way  the  formation  of  free  naphthenes  is  ex- 
plained. 

1  Cohen,  J.  B.,  and  Finn,  C.  P.,  Paraffin  from  Yorkshire  coal  seams.     Jour.  Soc.  Chem. 
Ind.,  Vol.  31,  p.  12,  1915. 

2  Hall,  A.  A.,  Oil  from  the  roof  of  the  Cockshead  coal  seam,  North  Staffordshire. 
Jour.  Soc.  Chem.  Ind.,  Vol.  26,  p.  1223,  1907. 

3  Bedson,  P.  P.,  Paraffin  wax  from  the  Ladysmith  Pit.     Jour.  Soc.  Chem.  Ind.,  Vol. 
26,  p.  1224,  1907. 

4  Jones,  D.  T.,  and  Wheeler,  R.  V.,  The  composition  of  coal.     Trans.  Chem.  Soc., 
Vol.  105,  p.  140,  1914. 


22  THE   CHEMICAL  PROPERTIES  OF  COAL 

Gases  in  Coal 

Gases  given  off  at  normal  temperatures.  —  In  many  coal  mines 
methane,  CH4,  (marsh  gas  or,  when  mixed  with  air,  fire  damp)  and 
carbon  dioxide,  CO2,  (choke  damp  or  black  damp)  are  found  in  large 
quantities.  Carbon  monoxide,  CO,  (white  damp)  occurs  in  lesser 
amounts  than  the  other  two  but  it  is  present  in  small  proportions 
in  many  mines.  The  quantity  of  gas,  consisting  chiefly  of  carbon 
dioxide  and  methane,  which  escapes  from  some  mines  is  very  great, 
running  into  many  thousands  of  cubic  feet.  What  is  regarded  as 
the  most  gaseous  mine  in  the  anthracite  region  of  Pennsylvania  has 
emitted  as  high  as  2400  cubic  feet  of  methane  per  minute. 

Experiments  have  shown  that  coals  will  absorb  gases  in  much  the 
same  way  as  charcoal  but  regarding  the  actual  condition  of  the  gas 
in  the  coal  before  mining  there  is  still  much  uncertainty.  Some 
investigators  have  considered  it  as  occluded  but  as  Porter  and  Ovitz1 
have  pointed  out  it  is  doubtful  whether  the  gas  exists  as  occluded  gas, 
or  in  a  condensed  condition,  in  the  true  sense  of  the  term  occluded. 
The  experiments  of  Chamberlin2  and  others  have  shown  that  the  coal 
gives  up  a  considerable  quantity  of  methane  and  some  ethane  when 
pulverized  but  only  a  small  percentage  of  that  given  off  if  the  coal  be 
allowed  to  stand  at  atmospheric  temperature  for  several  months  in 
vacuo  in  a  closed  vessel.  Porter  and  Ovitz  have  shown  that  although 
the  escape  of  methane  from  a  mine  seems  to  be  dependent  to  some 
extent  upon  the  atmospheric  pressure,  the  gas  from  broken  coal  after 
a  time  escapes  at  approximately  the  same  rate  under  atmospheric 
pressure  as  in  vacuo.  The  proportion  of  oxygen  in  the  gas  surround- 
ing the  coal  does,  however,  have  a  great  influence  on  the  rate  and 
amount  of  the  methane  given  off  without  causing  a  marked  effect 
upon  the  proportion  of  carbon  dioxide  set  free. 

From  a  practical  standpoint  these  conclusions  are  important 
because  ventilating  a  mine  carries  off  the  gas  set  free  but  it  also  fur- 
nishes more  oxygen  to  the  coal  and  thus  facilitates  the  escape  of 

1  Porter,  H.  C.,  and  Ovitz,  F.  K.,  The  escape  of  gas  from  coal.     U.  S.  Bur.  of  Mines, 
Tech.  Paper  2,  191 1.     Also  Parr  S.  W.,  and  Barker,  P.,  The  occluded  gases  in  coal.     Uni- 
versity of  111.,  Bull.  No.  20,  Vol.  VI,  1909. 

2  Chamberlin,  R.  T.,  Notes  on  explosive  mine  gases  and  dusts  with  special  reference 
to  the  explosions  in  the  Monongala,  Darr  and  Naomi  coal  mines.    U.  S.  Geol.  Survey, 
Bull.  383,  1909. 


GASES  EVOLVED   FROM   COAL  23 

deleterious  gases.  The  amount  of  gas,  both  methane  and  carbon 
dioxide,  given  off  from  coal  which  has  been  mined  varies  greatly  with 
different  coals,  but  in  practically  all  cases  the  proportion  given  off 
during  the  first  few  days  is  much  greater  than  that  which  escapes  with 
an  increase  in  the  length  of  time  during  which  the  experiment  is  con- 
tinued. The  loss  of  gas  is  usually  complete  in  from  three  to  eighteen 
months  and  the  deterioration  in  heating  value  is  small.  When  coal 
absorbs  methane  it  gives  up  nitrogen  somewhat  less  in  amount  than 
the  volume  of  methane  absorbed1. 

Gases  evolved  from  coal  heated  below  temperature  of  decom- 
position. —  In  addition  to  the  gases  given  off  in  the  coal  seams  at 
atmospheric  temperature  and  pressure  considerable  quantities  are 
driven  out  of  the  coal  by  heating  it  to  a  point  a  little  below  the  tem- 
perature at  which  decomposition  begins.  In  view  of  the  effect  of 
the  absorption  of  oxygen  on  the  gases  given  off  it  seems  probable  that 
the  increase  of  temperature  not  only  expels  the  gas  because  of  increas- 
ing the  volume  but  that  it  aids  chemical  action  to  a  slight  degree. 
In  peat  the  gases  given  off  seem  to  consist  chiefly  of  nitrogen  and 
marsh  gas  with  smaller  amounts  of  carbon  dioxide.  The  presence  of 
the  nitrogen  is  probably  largely  the  result  of  air  being  imprisoned  in 
the  fuel.  The  oxygen  of  the  air  is  taken  up  by  carbon  or  hydrogen 
during  the  chemical  processes  accompanying  the  decay  of  the  vegeta- 
tion, leaving  the  nitrogen  free  in  the  peat. 

The  gases  from  lignite,  heated  to  100°  C.  in  vacuo,  consist,  so  far 
as  they  have  been  tested,  chiefly  of  carbon  dioxide  with  small  amounts 
of  carbon  monoxide,  nitrogen,  oxygen,  olefmes,  and  marsh  gas.  From 
cannel  coals  the  gases  are  largely  methane  and  carbon  dioxide.  In 
a  series  of  analyses  of  English  and  Scotch  cannels  Thomas2  shows  that 
when  they  are  heated  to  100°  C.  in  vacuo  they  give  from  16.8  to 
421.3  c.c.  of  gas  per  100  grams  of  coal  and  the  composition  of  the  gas 
varies  as  follows: 

CO2 6 . 44-84 . 55  per  cent. 

CH4 77 . 19-80. 69  per  cent.     Absent  in  three  samples 

C2He 2 . 67-7 . 80    per  cent.     Absent  in  two  samples 

C3H8 0.91  percent.     Present  in  one  sample  only 

C4Hio Not  present 

N2 5 . 96-46 . 06  per  cent. 

1  Katz,  S.  H.,  Absorption  of  methane  and  other  gases  by  coal.     U.  S.  Bur.  of  Mines, 
Tech.  Paper  147,  1917.     Also  McConnell,  W.,  Gases  enclosed  in  coal  and  coal  dust. 
Jour.  Soc.  Chem.  Ind.,  Vol.  13,  p.  25,  1894. 

2  Thomas,  J.  W.,  Jour.  Chem.  Soc.,  Vol.  30,  p.  144,  1876. 


THE   CHEMICAL  PROPERTIES  OF   COAL 


A  sample  of  Whitby  jet  yielded  30.2  c.c.  of  gas  consisting  of  CO2, 
10.93;  C4Hio,  86.90;  and  N2,  21.7  per  cent.  From  these  analyses 
it  is  seen  that  carbon  dioxide  is  present  in  all,  and  abundant  in  some 
coals.  Nitrogen  is  present  in  fairly  large  proportion  in  all  these 
coals  and  is  present  also  in  jet.  While  these  results  obtained  by 
Thomas  are  interesting  it  may  be  questioned  whether  they  can  be 
fully  relied  upon  in  view  of  the  difficulty  experienced  at  the  present 
day  with  more  modern  analytical  methods,  in  our  attempts  to  rec- 
ognize certain  of  these  rarer  gases. 

The  gases  obtained  from  bituminous  coal  and  anthracite  under 
the  conditions  stated  above  are  very  variable  in  amount  and  com- 
position. Von  Meyer1  found  ethane  up  to  23  per  cent  and  other 
undetermined  hydrocarbon  gases  in  small  amounts  in  some  Saxon 
and  Westphalian  coals.  From  the  works  of  W.  McConnell2  on  the 
coals  from  Newcastle  and  of  Thomas3  on  the  Welsh  coals  the  following 
figures  were  compiled: 

Volumes  of  gases  derived  from  100  grams  of  bituminous  coal  heated 
in  vacuo  at  100°  C.,  1.61  to  818  c.c.;  from  semibituminous  and  steam 
coal,  73.6  to  375.4  c.c.;  and  from  anthracite,  555.3  to  600.6  c.c.  The 
composition  of  the  gases  varied  as  follows: 


Semibituminous  and 
steam  coal 

Bituminous 

Anthracite 

C02  
CH4  and  other 
paraffins 
O2  

5  .04-1  8.  90  per  cent 

72.51-87.30 
0.33—  i  .02 

o  .  7  2-36  .  42  per  cent 

o  .  40-88  .  50 
0.80—  9  .41 

2.  62-14.  72  per  cent 
84.18-93.13 

N2  

3.49-14.62 

8.70-80.11 

1.  10-  4.25        '* 

The  paraffins  in  the  bituminous  coals  consisted  in  some  cases  almost 
entirely  of  methane  although  ethane  was  present  in  greater  or  lesser 
amount.  The  steam  coal  of  Seaton  Delaval  gave  off  no  hydrocar- 
bons, the  gas  consisting  entirely  of  carbon  dioxide,  oxygen,  and  nitro- 
gen. 

The  above  figures  go  to  show  that  in  anthracite  the  predominant 
gas  is  methane,  while  in  the  lower  types  of  coal  carbon  dioxide,  nitro- 

1  Quoted  by  F.  W.  Clarke,  Op.  cit,  p.  759. 

2  Op.  cit. 

3  Thomas,  J.  W.,  Jour.  Chem.  Soc.,  Vol.  28,  p.  793,  1876. 


PRODUCTS  OF  DISTILLATION  25 

gen  and  methane  form  the  main  constituents  of  the  gas.  This  is 
further  illustrated  by  the  fact  that  if  heated  to  higher  temperatures 
but  still  below  the  point  of  decomposition  the  relative  proportion  of 
methane  increases  while  that  of  nitrogen  decreases.  The  longer  the 
coal  is  heated  the  more  gas  is  given  off,  this  being  especially  true  of 
hard  compact  coals  such  as  anthracites.  The  bulk  of  the  gas,  however, 
is  evolved  early  in  the  experiment. 

Relation  of  mine  gases  to  volatile  constituents  in  coal.  —  The 
proportion  of  volatile  matter  in  coal  seems  to  have  little  or  no  relation 
to  the  percentage  of  gas  evolved  on  heating  below  the  temperature 
of  decomposition  and  the  explosibility  of  mine  gases  and  dusts  seems 
to  depend  much  more  upon  the  nature  of  the  gases  evolved  than  upon 
the  relative  percentage  of  volatile  matter  in  the  coal. 

Analyses  made  by  Thomas  of  the  gases  from  blowers  in  coal  seams 
and  of  those  gases  obtained  from  the  seam  by  boring  show  that  there 
is  little  difference  between  them.  In  some  blowers  the  oxygen  reaches 
over  10  per  cent  and  nitrogen  over  41  per  cent  of  the  gas,  but  oxygen 
is  lacking  in  many.  Carbon  dioxide  is  less  than  i  per  cent  in  nearly 
all,  while  marsh  gas  constitutes  over  90  per  cent  of  the  gases  derived 
from  practically  all  blowers  and  borings  in  the  seams. 

Products  o   Distillation 

The  chief  products  resulting  from  the  distillation  of  coal  are  coke, 
tar,  light  oils,  water  of  decomposition,  and  a  mixture  of  gases  con- 
sisting chiefly  of  NH3,  H2S,  H,  C02,  CO,  unsaturated  hydrocarbons, 
and  CnH2n+2.  The  processes  of  distillation  and  the  chemistry  of 
the  resulting  products  are  subjects  which  are  so  complex  that  a  de- 
tailed discussion  of  them  involves  a  treatment  of  the  subjects  of  gas 
manufacture,  the  dye  industry,  and  many  other  related  problems. 

(Fig.  5)1- 

The  relative  proportions  of  the  volatile  constituents  obtained 
depend  upon  many  factors,  such  as  the  kind  of  coal  and  the  con- 
ditions under  which  the  coal  is  heated,  including  the  temperature,  the 
pressure  and  the  length  of  time  involved.  It  has  also  been  found  that 

1  For  detailed  descriptions  of  experiments  and  conclusions  regarding  the  volatile 
matter  in  coal,  see  Porter,  H.  C.,  and  Ovitz,  F.  K..  The  volatile  matter  of  coal.  U.  S. 
Bur.  of  Mines,  Bull,  i,  1910;  and  The  primary  volatile  products  of  the  carbonization  of 
coal.  Tech.  Paper  140,  1916.  Also  Rittman,  W.  F.,  and  Whitaker,  M.  C.,  A  bibliog- 
raphy of  the  chemistry  of  gas  manufacture.  U.  S.  Bur.  of  Mines,  Tech.  Paper  120,  1915. 


26 


THE   CHEMICAL  PROPERTIES  OF  COAL 


a  wet  coal  will  produce  a  greater  ammonia  yield  and  less  gas,  but  a 
gas  richer  in  hydrocarbons,  than  a  dry  coal. 

Effect  of  temperature  on  quantity  and  kind  of  constituents 
evolved.  —  The  experiments  of  Porter  and  Ovitz  have  shown  that, 
as  a  rule,  more  than  two-thirds  of  the  organic  substances  are  de- 
composed at  temperatures  below  500°  C.  It  is  probable  that  some 
change  takes  place  in  exposed  coal  at  atmospheric  temperatures  but 
appreciable  quantities  of  volatile  matter  are  given  off  from  most 
coals  at  250°  C.  In  a  series  of  experiments  on  bituminous  coals 
Burgess  and  Wheeler1  found  that  occluded  or  " condensed"  gases 
which  are  unextractable  at  atmospheric  temperatures  are  extracted 
in  vacuo  by  heating  from  150°  to  200°  C.  These  gases  consist  mainly 
of  the  higher  members  of  the  paraffin  hydrocarbons.  The  following 
table  shows  the  quantity  of  gas  and  its  composition  evolved  from  100 
grams  of  coal  heated  to  100°  C.  and  the  same  amount  heated  to  200°  C. 


Temperature 

Volume  of  gas 

Composition  per  cent 

C02 

0, 

OH, 

CH2n(n72) 

CO 

H, 

C.H2n+2 

100° 
200° 

34  c.c. 
65.5  c.c. 

6.70 
8.85 

1-65 
0.70 

0.85 
0.85 

1.30 
2  .90 

1.40 
2.6o 

1.90 

2-75 

84.55 
Sl.OO 

Of  the  gas  obtained  at  200°  about  7.5  per  cent  consisted  of  butane. 
The  identification  of  this  gas  has,  however,  been  called  in  question 
by  some  chemists. 

The  younger  coals  of  the  western  and  middle-western  states  break 
down  more  quickly,  as  a  rule,  than  the  Appalachian  coals.  This 
greater  ease  of  disintegration  is  probably  related  to  the  proportions 
of  resinous  and  cellulosic  constituents,  the  older  coals  yielding  a 
larger  proportion  of  hydrocarbon  constituents  from  the  resinous 
materials  and  the  less  mature  coals  a  greater  proportion  of  carbon 
dioxide  and  water.  The  early  products  of  distillation  are  mostly 
CO2,  CO,  and  H2O  and  these  come  off  slowly  up  to  450°  C.  At  this 
temperature  the  products  of  the  lower  grades  of  coal  are  mostly  water 
and  carbon  dioxide,  and  those  from  bituminous  coal  largely  members 

1  Burgess,  M.  J.,  and  Wheeler,  R.  V.,  The  distillation  of  coal  in  a  vacuum;  Trans. 
Chem.  Soc.,  Vol.  105. 


EFFECT  OF  TEMPERATURE  27 

of  the  paraffin  series,  with  gases  of  the  series  CnH2n+2,  higher  than 
CH4,  predominating  below  400°  C.  Water  of  decomposition  is  ex- 
pelled much  more  rapidly  between  250°  C.  and  500°  C.  than  at  a 
higher  temperature. 

Sulphurous  gases,  such  as  H2S,  begin  to  be  formed  at  250°  C.  and 
the  production  rises  to  a  climax  more  rapidly  than  that  of  hydrogen 
or  the  hydrocarbons.  The  thermal  decomposition  of  the  volatile 
matter  takes  place  very  readily  at  temperatures  above  750°  C.  and 
the  percentage  of  hydrogen  and  the  hydrocarbons  increases,  with 
hydrogen  predominating,  at  the  higher  temperatures.  The  increase 
of  these  gases  takes  place,  however,  at  the  expense  of  the  tar,  which 
has  been  increased  13  per  cent  in  yield  from  Pittsburgh  coal  by  heat- 
ing it  below  500°  C.  rather  than  at  the  usual  temperature  employed 
in  carbonizing  coal.  It  is  evident  that  the  composition  of  the  tar 
obtained  at  the  different  temperatures  will  vary  considerably.  At 
900°  C.  the  volatile  matter  is  practically  all  expelled  from  a  coal  of 
the  Pittsburgh  type  although  heated  only  a  few  seconds,  which  is 
the  time  necessary  to  raise  the  temperature  to  that  point. 

The  experiments  of  Burgess  and  Wheeler1  in  England  produced 
results  for  low  temperature  distillation  gases,  very  similar  to  those 
described  above,  but  these  authors  concluded  that  there  is  a  decompo- 
sition point  between  700°  and  800°  C.  at  which  hydrogen  is  distilled 
at  a  marked  increase  in  rate.  This  change  is  considered  as  indicating 
the  presence  in  the  coal  of  two  types  of  compounds,  one  type  decom- 
posing at  a  lower  temperature  than  the  other  and  yielding  mostly 
hydrocarbons  in  contrast  to  the  other  which  yields  hydrogen  as  the 
chief  decomposition  product.  Although  Porter  and  Ovitz  found  that 
hydrogen  was  given  off  in  greater  proportions  above  750°  C.  they  do 
not  consider  that  any  line  of  demarcation  may  be  drawn  near  this 
point  which  would  indicate  the  decomposition  of  distinct  compounds. 

1  Burgess,  M.  J.,  and  Wheeler,  R.  V.,  The  volatile  constituents  of  coal.  Jour.  Chem. 
Soc.,  Vol.  97,  p.  1917,  1910;  Vol.  99,  p.  649,  1911.  Clark,  A.  H.,  and  Wheeler,  R.  V., 
The  volatile  constituents  of  coal.  Jour.  Chem.  Soc.,  Vol.  103,  p.  1704,  1913. 


28 


THE   CHEMICAL   PROPERTIES  OF   COAL 


By-product  tests  on  coals: 

TABLE  SHOWING  RESULTS  OF  BY-PRODUCT  TESTS 
ON  VARIOUS  COALS1 


Number  of  Samples 

16 

3 

23 

ii 

ii 
(Air-dried) 

25 

46 

Number  of  tests 

averaged.  .  .  . 

2 

2 

4 

2 

2 

2 

Coke,  per  cent.  .  . 

79-i 

71-4 

63.1 

44-7 

53-o 

58.6 

63.9 

Tar,  per  cent  .... 

7.2 

n-3 

II-9 

7-i 

5-5 

12.3 

10.3 

Water,  per  cent  . 

i-3 

4-9 

10.7 

27-5 

19.0 

ii.  8 

IO.O 

Ammonia,  pounds 

of  sulphate  per 

ton 

12    Q 

23    8 

2C     2 

27    ^ 

26    7 

26  i 

26     7 

CO2,  per  cent.  .  .  . 

j 
0.44 

*o  *  w 

0.72 

o  •  o 
1.20 

•^  /  •  — 

8.14 

^.\J  .    j 

8.41 

*\>  .  ^ 
3-i3 

'v  ••} 

2.13 

H2S,  per  cent.  .  .  . 

O.O7 

0.25 

0.46 

0.08 

O.II 

0.24 

0.30 

Gas,   cu.   ft.   per 

ton  (a) 

Q.7OO 

8,140 

8.4OO 

7,8^0 

8,170 

7,620 

7  Q4.O 

Composition  of 

y  »  /  ***• 

^>  AiJ.W 

U,£f.\SW 

/  J^O 

Uf  ft  y  W 

^   )\J  4\S 

/  >:7T-W 

gas  (6)  .  .      . 

Illuminants  

1.4 

3-2 

3-o 

2  .2 

2.6 

5-7 

5-5 

CO  

3-2 

S-i 

7-4 

!9-5 

21.4 

14-9 

12.3 

CH4,  C2H6,  etc.  .  . 

26.4 

27.8 

26.3(C) 

18.1 

22.6(C) 

27.2 

25.4 

H  

67.8 

6r.o 

56.8(c) 

^4  o 

4Q.  2(^) 

47.8 

C2      I 

N  

I  .2 

2-9 

6-5 

OT-  *  ^ 
6.2 

T^^'O   \       / 

4-i 

4-4 

oo 
3-7 

Value  of  "n"  in 

CnH2n+2  

(*) 

1.27 

(*) 

1.18 

(«) 

1.32 

1.29 

Total        volatile 

products  with- 

out moisture.  .  . 

19-7 

27.4 

29.8 

33-3 

35-5 

38.5 

32.4 

Water  of  consti- 

tution   

O.I 

3-7 

3-6 

5-5 

7-5 

8.9 

6-3 

Inert     volatile 

matter  (d)  

0.7 

4-7 

5-i 

14.0 

16.3 

12.4 

8.8 

(a)  Calculated  to  dry  basis  at  o°  C.  and  760  mm.  pressure,  free  of  air  and 
carbon  dioxide.  (6)  Calculated  to  carbon  dioxide  and  oxygen-free  basis,  (c) 
Hydrogen  not  determined  separately  by  palladium  but  calculated  from  com- 
bustion: Methane  probably  high  and  hydrogen  low.  (d)  Sum  of  carbon  dioxide, 
ammonia  and  water  of  constitution. 

The  coals  used  in  these  tests  were  as  follows:  No.  16,  Pocahontas; 
No.  3,  Connellsville;  No.  23,  Harrisburg,  111.;  No.  n,  Sheridan, 
Wyoming  subbituminous  coal;  No.  25,  Utah  bituminous  coal;  No. 
46,  Wyoming  bituminous  coal. 

Burgess  and  Wheeler2  distilled  anthracite  at  900°  C.  for  varying 

1  Porter  and  Ovitz,  U.  S.  Bur.  of  Mines,  Bull.  I,  p.  26,  1910.  See  also  Church,  S.  R., 
Methods  for  testing  coal  tar  and  refined  tars,  oils,  and  pitches  derived  therefrom.  Jour. 
Ind.  and  Eng.  Chem.,  Vol.  3  p.,  227,  1911. 

2  Burgess,  M.  J.,  and  Wheeler,  R.  V.,  The  volatile  constituents  of  coal,  Pt.  II.  Trans. 
Chem.  Soc.,  Vol.  99,  pp.  665-6,  1910. 


=1— . 


.'GOIM 


GAS  LIQUOR         | 


ilSULFID       BEN20'-        TOLUOL          XYLOL 


II  SULFUR  JICYANOOEN|{ 
"  "  'I 


AMMONIUM  AMMONIUM        JJ        AMMONIUM  AMI^ 

_SULFATE       II          NITRATE         Ij       CARBONATE        ||         CARP 


I         SULFOCYANIDE          |      |        FERROCYANIDE 


f        FERRICYANIDE         |  |       PRUSSIAN  BLUE         ) 


LIGHT  OIL 


MIDDLE  OIL 


I      C""«jr°"«        ||.«UT,,LO,U,|     | 

1 

|            PAINT  THINNERS        |  [      *", 

I  

|    PHENOL    |        CRE80L      |      I  BA.  .    [.  ,,.    | 

1 

P"HTE 

^NO'L'     1 

h'REslNS-||^S-S-      ||    j*W         | 

RA 

L^^'N||8AL,C^?C\CIDllk^ 

1   DYE  STJFF8  |  |      FLAVORINGS       I 

1     PMENACETIN      |  Lg 

fffr.    |P 

«fc 

PICRIC      I 

L 

DYE  STUFFS 

1       I 

XPLOSIVES     ^ 

r- 

HEA 


I  CRUDE 

NAPHTHALIN  | 


8HiNGLE      I  I         NARPEHFTHALIN  I    |     PHENOL     ||cRESOL|[ 


PXTHALICAC1D     j        NAPHTHOU8 


{    NAPHTHOU8    | 

EZTJ__ 

SDLE 


INDIGO 


1AMIDO  NAPHTHOL       I  Pi 
8ULFOACID  1 1 


|       PHENOL      ~\          j        CRE80L8         [  I        PORE  TOLUOL 


LOY^^Fr,    j|     SOLVENT     |   |          "JTROin^ 


I        EXPLOSIVES       I         j    TOLUIDir 


II   "gffl  I  L_ 


I  HMOJ          I      |     PMOTOaRAPMY"^  |          DYE  8TUFM        ||         ANTPYRIN 


»T6STI!)F.F»       I  INDIGO 


FIG.  5    Distillation  products  of  coal  and  their  commerci 


>AL 


|        COKE 

1          AMMONIUM.         1 
«_||           CHLORIDE         | 

1                    1 

1                                                                                  1 

!             1        - 

_                 |       ELECTRODES     ||    LAMP  BLACK    |                      |        LUBRICANT        j          CRUCIBLES       ||       ELECTRODES       | 

i'lL 

REFINED  TAR                                          PITCH 

j          PRES^TION       1         *™C1N       |  |    LAMP  . 

LACK                          PAINTS               TARRED  FELT    |         P'PE                        SUB                        SIDEWALK                   PAVING 
1  1      WITH  p,TCH    II     COATING      ||     FLOORING     ||        COMPOSITION        ||MATERIALS 

F~l           1          iM^SoN          I 

I  1  

.__                                                                                                TAR-ROK                           1       TARVIA        1 

1        PRESERVATION         1                  1            CEASES 

ANTHRACIN          | 

.Kg         |    1          °^NTAN£           j                                  |  

|                         SHINGLES       ||              ROOFING              II  HOOFING  |l      TION         (PROOFING    | 

|      CARBOZOL      |j 

PHENANTHRIN      |  |        ANTHRACIN 

JANTHRA- 
1             QU.NONE           1 

1 

JLPHOUACI°SE                                         QUINAZARIN 

J  , 

1 

DYE  STUFFS        | 

1                  ALIZARIN 
DYE  STUFFS 

1             1                   ALGOL                   I 
I              1              DYE  STUFFS              I 

SOFT  PITCH 

,                                                                                                  1 

,                 1                                    1 

INSULATION                1       p^J^L                           PAVING                                          MEDIUM 

|                                         III 

'  ACID       |      |             BENZOLDEHYDE 

|          BRIQUETS         |      |       PA.NTS       |    |      ROOFING      |     |       pRVATERQ        |    |        HARD  p 

ITCH;     1 

^n 

1 

i 

•YE  STUFFS          |      PERFUMES      11      BEANC2,°'C      | 

BRIQUETS      II     coJ^J^g      ||    ELCEACR70°ND8E8    ||      TARGETS      1  1  POWD.  FUEL  1  1           PITCH 

*                     •»»           « 

i  —  !  "  "  '    T    ' 

|            METAL  CASTING            j                                                                                        |           FUEL           | 

r                          L_ 

1         ""FUMES                                  |         .88m. 

m 

FOOD 
1  PRESERVATIVE             | 

es.     (Reproduced  by  permission 

of  the  Barrett  Company.) 

HAT 


1 


~ 

L  i ..;„.-.  i^  _ 


THE   SOLUBILITY  OF   COAL  AND   ITS   DESTRUCTION  BY   ACIDS    29 

periods  of  time  and  recorded  the  results  for  periods  of  five  seconds 
each.  During  the  first  five  seconds  6.65  c.c.  of  gas  at  o°  C.  and  760 
mm.  were  evolved,  and  during  the  tenth  five-second  period  20.95  c-c- 
The  composition  of  the  gas  taken  at  the  periods  mentioned  was  as 
follows  —  when  calculated  on  a  " nitrogen-free "  basis: 

A  B 

NH3 6.10 0.20 

C6H6 3-80 o-35 

H2S 2.75 0.35 

CO2 9.85 1.40 

C2H2 0.30 nil 

C2H4 2.35 nil 

CO 16.65 ••••  5-6o 

H2 31-20 82.30 

CH4 25.95 8-4o 

C2H6 1. 10 1.35 

The  tarry  products  derived  from  the  distillation  of  coal  are  of  great 
industrial  importance  and  their  derivatives  are  obtained  by  numerous 
chemical  processes,  some  of  which  are  of  remarkable  complexity.1 
The  following  plan  shows  the  main  products  derived  from  coal  and 
it  sets  forth  the  relations  among  these  various  compounds.  (Fig.  5.) 

The  Solubility  of  Coal  and  its  Destruction  by  Acids 

The  degree  of  solubility  of  different  coals  varies  greatly  owing 
to  the  fact  that  they  are  not  homogeneous  and  their  resinous  con- 
stituents will  dissolve  much  more  readily  in  some  reagents  than  their 
cellulosic  constituents.  Coals  which  contain  much  humic  acid  will 
dissolve  to  a  considerable  extent  in  alkaline  solutions,  while  the 
cellulosic  constituents  may  be  attacked  by  nitric  acid.  Most  of  the 
resinous  constituents  are  soluble  to  some  extent  in  organic  solvents 
such  as  benzine. 

Peat  and  the  xyloid  lignites  are  partially  soluble  in  caustic  alkalies 
and  almost  completely  soluble  in  alkaline  hypochlorites.  The  com- 
pact lignites  or  subbituminous  coals  are  readily  attacked  by  the  al- 
kaline hypochlorites  but  are  only  slightly  soluble  in  caustic  alkalies, 
while  bituminous  coals  and  anthracite  are  not  dissolved  by  alkaline 
solutions.  Dilute  nitric  acid  will  attack  lignite  and  strong  acid  will 
slowly  attack  the  higher  coals  but  a  mixture  of  nitric  and  sulphuric 

1  Hoffman,  A.  W.,  Etudes  sur  les  matieres  colorantes  derivees  du  goudron  de  houille 
Compt.  Rend.,  Vol.  55,  pp.  781,  805,  817,  849  and  901, 1862,  and  Vol.  56,  pp.  1033  and  1062. 


THE   CHEMICAL  PROPERTIES   OF   COAL 


acids  will  completely  break  down  the  more  reshtant  coals  leaving  a 
deep  brown  solution  from  which  the  coloring  matter  is  precipitated 
on  the  addition  of  water.1 

By  the  action  of  nitric  acid  on  finely  pulverized  coal  Guignet2  ob- 
tained oxypicric  acid  and  a  mixture  of  oxide  of  iron  and  sulphuric 
acid  resulting  from  the  pyrite  in  the  coal.  By  boiling  the  mixture 
in  water  with  barium  carbonate  the  oxide  of  iron  and  the  oxalic  and 
sulphuric  acids  were  thrown  out  while  the  oxypicrato  of  barium  re- 
mained. On  precipitating  the  barium  as  sulphate,  crystals  of  oxy- 
picric  acid  remained.  There  were  left  on  filtering  the  original  nitric 
acid  solution  compounds  which  were  insoluble  and  which  exploded 
when  heated. 

Most  of  the  resinous  compounds  in  coal  are  partially  soluble  in 
the  strong  acids,  they  are  partially  or  entirely  soluble  m  alcohol, 
and  most  of  them  partially  so  in  ether  and  in  turpentine.  The  sol- 
vent action  of  benzine  is  variable.  It  is  thus  evident  that  the  pro- 
portion of  resinous  constituents  in  coal  will  affect  to  a  considerable 
extent  its  solubility  in  various  solvents. 

Relation  of  solubility  to  coking  qualities.  —  The  results  of  Vig- 
non's3  work  show  that  there  is  some  definite  relation  between  the 
composition  of  the  coal,  its  solubility  in  various  organic  solvents  and 
incidentally  its  coking  quality.  The  coals  from  the  Loire  region 
showed  the  following  results  when  treated  with  aniline.  Taking 
fat  gas  coals,  semi-fat  coals,  and  lean  or  dry  coals  he  obtained  the 
following  results: 


Initial  weight 

Weight  after 
treatment    with 

Percentage 

Percentage 
soluble,  ash 

aniline 

deducted 

(i)  Fat  gas  coal.  .  . 
(2)  Semi-fat  coal.  . 

1.46-1.68 
1.17-1.32 

I  .12-1  .29 
I  .09-1  .23 

23.40 
6.58 

26.8 
7.2 

(3)  Lean     or     dry 

coal  

2  .  17—2  .OI 

2  .  14—2  .OI 

1.56 

1.8 

1  Fremy,  E.,  Recherches  chimiques  sur  les  combustibles  mineraux.     Compt.  Rend., 
Vol.  52,  pp.  114-117,  1861. 

2  Guignet,  E.,  Sur  la  constitution  de  la  houille.     Compt.  Rend.,  Vol.  88,  pp.  590-592, 
1879- 

3  Vignon,  Leo,  Sur  les  dissolvants  de  la  houille.     Compt.  Rend.  VoL  158,  pp.  1421- 
1424,  1914. 


RELATION  OF   SOLUBILITY  TO   COKING  QUALITIES 


The  portion  of  the  coal  which  is  soluble  is  richer  in  hydrogen  than 
the  insoluble  portion  and  from  this  it  may  be  inferred  that  the  coking 
coals  will  differ  from  non-coking  coals  in  their  solvent  action  with 
aniline. 

On  treating  coal  with  alcohol,  ether,  benzine,  toluene,  aniline  and 
nitro-benzine,  Vignon  obtained  the  following  results  with  50  c.c. 
of  the  solvent  and  10  grams  of  coal. 


Soluble  at  ordinary  temperature  for 
24  hours 

Soluble  at  boiling  point  for  3  hours 

Alcohol 

0.076  per  cent 

0.0167  per  cent 

Ether 

0.059 

Benzine                .... 

0.080       ' 

0.191 

Toluene.         

0.078 

0.190       " 

Aniline  
Nitro-benzine  

2.250 
i  .410 

12.050 
3-190 

From  this  table  it  is  evident  that  aniline  js  the  most  active  solvent 
for  these  bituminous  coals  of  the  Loire  basin.  Of  the  other  common 
solvents  pyridine  and  phenol  may  be  regarded  as  the  most  active. 
Clark  and  Wheeler1  claim  that  a  coal  may  be  divided  into  two  types 
of  compounds  recognized  by  their  differential  solvent  action  with 
pyridine  and  chloroform,  one  of  these  compounds  being  higher  in 
hydrogen  and  the  other  in  hydrocarbons. 

Phenol  has  been  employed  as  a  solvent  for  coal  by  a  number  of 
chemists,  but  the  first  extensive  experiments  to  determine  the  deriva- 
tives of  the  solution  with  phenol  were  carried  out  by  Parr  and  Hadley2 
and  by  Frazer  and  Hoffman.3  The  latter  authors  found  that  10.87 
per  cent  of  an  Illinois  non-coking,  bituminous  coal  was  dissolved  in 
phenol.  From  this  solution  a  large  number  of  derivatives  were 
extracted,  some  of  which  are  believed  to  be  pure  compounds.  Parr 
and  Hadley  found  that  there  is  a  distinct  relation  between  the  per- 
centage of  the  coal  dissolved  in  phenol  and  its  coking  qualities.  The 
coking  constituents  are  almost  all  dissolved  in  this  solvent  and  oxi- 

4  Clark,  A.  H.,  and  Wheeler,  R.  V.,  Op.  cit. 

2  Parr,  S.  W.,  and  Hadley,  H.  F.,  The  analysis  of  coal  with  phenol  as  a  solvent,  Uni- 
versity of  111.,  Bull  No.  10,  Vol.  XII. 

3  Frazer,  J.  C.  W.,  and  Hoffman,  E.  J.,  The  constituents  of  coal  soluble  in  phenol. 
U.  S.  Bur.  of  Mines,  Tech.  Paper  5,  1912. 


32  THE   CHEMICAL  PROPERTIES  OF   COAL 

dation  of  the  coal  greatly  affects  its  relative  solubility.     This  solvent 
was  also  used  to  extract  organic  sulphur. 

Chemical  Causes  of  Spontaneous  Combustion1 

There  has  been  a  great  deal  of  speculation  regarding  the  cause  of 
spontaneous  combustion  of  coal  and  many  have  assigned  it  to  the 
oxidation  of  pyrite.  It  is  now  recognized,  however,  that  while  the 
oxidation  of  pyrite  and  the  action  of  the  sulphuric  acid  on  moisture 
in  the  coal  may  produce  some  heat,  the  fundamental  cause  of  the 
heating  is  the  oxidation  of  the  coal  itself.  The  sulphuric  acid  re- 
sulting from  the  oxidation  of  pyrite  is  a  powerful  oxidizing  agent  and 
its  presence  facilitates  oxidation  of  the  coal,  but  coal  itself  will  oxidize 
rather  rapidly  for  a  time  after  mining.  If  there  is  a  good  circulation 
of  air  it  will  not  take  fire  but  if  there  is  only  a  partial  supply  of  air 
oxidation  goes  on  and  the  heat  is  retained.  As  the  temperature  of 
the  fuel  rises  the  rate  of  oxidation  is  greatly  accelerated  and  in  con- 
sequence there  is  cumulative  action  progressing  towards  the  tempera- 
ture of  combustion  which  varies  from  about  300°  C.  upward  depending 
upon  the  character  of  the  coal.  According  to  Fayol  finely  powdered 
lignite  may  ignite  at  a  temperature  as  low  as  150°  C.  and  gas  coal 
at  200°  C. 

There  is  a  fairly  definite  relation,  as  shown  by  Wheeler,2  between 
the  temperature  of  ignition  of  coal  dust  and  the  proportion  of  its 
resinous  constituents,  which  are  soluble  in  pyridine. 

The  oxidation  process  goes  on  in  both  moist  and  dry  coals,  although 
moisture  aids  the  process  very  greatly.  If  the  coal  be  completely 
covered  with  stagnant  water  oxidation  almost  ceases  after  a  bref 
time  but  circulating  water  may  bring  in  new  supplies  of  oxygen  to  le 
coal.  The  finer  the  coal,  the  more  rapid  is  the  oxidation  of  a  given 
surface,  other  things  being  equal.  The  percentage  of  volatile  matter 

1  Parr,  S.  W.,  and  Kressmann,  F.  W.,  The  spontaneous  combustion  of  coal.    Univer- 
sity of  111.,  Bull.  16,  1910. 

Moissan,  H.,  Traite  de  chimie  minerale,  Vol.  2,  pp.  363-364,  1905,  (on  spontaneous 
combustion). 

Stansfield,  E.,  An  investigation  of  the  coals  o*  Canada.  Vol.  6,  Dept.  of  Mines,  Canada, 
1912. 

Hapke,  L.,  The  causes  and  prevention  of  spontaneous  combustion.  Chem.  Zeit. 
17,  p.  916,  1893. 

2  Wheeler,  R.  V.,  The  volatile  constituent?  of  coal,  Pt.  IV:   The  relative  inflamma- 
bilities of  coal  dusts.    Trans.  Chem.  Soc.,  Vol.  103,  p.  1715,  1913. 


SULPHUR  33 

seems  to  make  little  difference  in  the  spontaneous  heating  as  all 
types  of  coal  have  been  known  to  heat.1  There  are,  however,  no 
authentic  cases  reported  where  anthracite  has  actually  taken  fire  in 
storage.  The  natural  process  of  heating  is  often  accelerated  by  the 
proximity  of  the  coal  bins  to  furnaces  and  other  sources  of  heat  and 
this,  no  doubt,  explains  why  coal  on  shipboard  and  in  other  places 
adjacent  to  boilers  often  takes  fire  while  in  the  bins. 

A  certain  amount  of  loss  in  the  heating  value  of  coal  takes  place 
during  weathering  and  the  accompanying  oxidation.  This  may  be 
readily  understood  when  the  results  of  White's  investigations  are 
considered,  since  he  found  oxygen  and  ash  to  be  of  almost  equal  anti- 
calorific  value.2  Further,  the  loss  of  methane  accompanies  the  oxi- 
dation process  and  the  heating  value  of  this  gas  amounts  to  a  small 
item. 

Source  of  Mineral  Constituents 

The  source  of  many  of  the  constituents  of  coal  is  self-evident  when 
the  composition  of  wood  is  considered.  The  carbon,  hydrogen, 
oxygen,  and  nitrogen  may  all  be  derived  directly  from  the  wood  but 
there  are  many  other  constituents  whose  source  and  whose  condition 
in  the  coal  are  not  so  readily  recognized.  In  addition  to  the  nitrogen 
in  wood,  which  varies  from  less  than  i  per  cent  to  over  3  per  cent, 
some  is  supplied  by  animal  matter  and  it  is  probable  that  a  little  is 
added  to  the  coal  from  the  air  through  its  imprisonment  in  the  vege- 
tation before  it  becomes  coal. 

Sulphur.  —  Sulphur  is  a  constituent  of  considerable  economic  im- 
portance in  coal  because  it  reduces  the  quality  of  coke  for  metallurgical 
purposes,  it  increases  corrosion  of  boilers  and  in  quantities  of  more 
than  about  2  per  cent  it  increases  clinkering  in  furnaces  by  aiding 
the  fusion  of  ash.  This  2-per  cent  limit  will  vary,  however,  with  the 
varying  proportions  of  ash  and  sulphur  present  and  it  is  probable 
that  the  iron  combined  with  the  sulphur  in  pyrite  may  aid  the  fusi- 
bility of  the  ash  almost  as  much  as  the  sulphur.  In  coking  approxi- 
mately one-half  of  the  sulphur  in  the  coal  is  supposed  to  enter  the 
coke.  This  proportion  will  apparently  vary  with  the  proportion  of 

1  Porter,  H.  C.,  and  Ovitz,  F.  K.,  Deterioration  and  spontaneous  heating  of  coal 
in  storage.     U.  S.  Bur.  of  Mines,  Tech.  Paper  16,  1912. 

2  White,  D.,  The  effect  of  oxygen  in  coal.     U.  S.  Geol.  Survey,  Bull.  382,  1909. 


34  THE   CHEMICAL  PROPERTIES  OF  COAL 

organic  and  inorganic  sulphur.  While  one  molecule  of  the  sulphur 
in  pyrite  (FeS2)  may  be  removed  in  the  burning  process  leaving  the 
other  to  enter  the  coke  with  the  iron,  this  relation  will  not  hold  for 
the  proportions  of  organic  sulphur,  the  compounds  of  which  are  not 
so  well  known. 

Sulphur  occurs  in  varying  amounts  in  coal,  from  less  than  i  per 
cent  to  10  per  cent  or  more.  It  commonly  amounts  to  between  one- 
half  of  i  per  cent  and  3  per  cent  although  many  of  the  coals  of  our 
middle-west  states  carry  between  3  and  5  per  cent.  The  sulphur  is 
in  two  forms:  organic  and  inorganic.  The  inorganic  type  is  most 
familiar  and  it  occurs  in  the  following  forms:  (i)  Mineral  sulphides, 
(2)  Sulphates  and  (3)  Free  sulphur. 

Inorganic  sulphur.  —  Of  the  sulphides  iron  pyrite  (FeS2,  Isometric) 
and  marcasite  (FeS2,  Orthorhombic)  are  the  most  common.  Chal- 
copyrite  (Cu'FeS2),  arsenopyrite  (FeAsS),  stibnite  (Sb2S3)  and  a  few 
other  sulphides  have  been  found  but  they  are  rare  except  in  some 
regions  where  volcanic  activity  has  occurred.  Pyrite  or  iron  pyrites, 
also  known  as  " fools'  gold"  is  responsible  for  most  of  the  "sulphur 
balls,"  "coal  brasses,"  and  "sulphur  diamonds"  found  in  coal  seams 
although  marcasite  frequently  occurs  in  sulphur  balls  and  is  mis- 
taken for  pyrite  since  many  people  do  not  distinguish  these  two 
minerals  from  each  other.  The  sulphide  occurs  in  largest  quantities 
in  concretions,  commonly  known  as  "sulphur  balls,"  in  lenses  or 
bands  running  parallel  with  the  coal  seam  or  in  veinlets  cutting  across 
the  seam.  When  in  sufficiently  large  quantities  it  is  separated  from 
the  coal  in  mining  and  at  some  mines  it  is  sold  for  the  manufacture 
of  sulphuric  acid.  In  addition  to  the  masses  of  pyrite  which  are  so 
evident  to  the  naked  eye,  Thiessen1  has  shown  that  in  practically  all 
coals  and  also  in  peat  there  are  numerous  grains  of  pyrite  averaging 
25  to  40  microns  in  diameter,  distributed  through  the  fuel  (Fig.  6). 
These  appear  to  be  more  abundant  in  the  xyloid  bands  in  the  coal 
and  it  seems  quite  probable  that  at  least  part  of  the  pyrite  has  been 
formed  by  combination  of  iron  with  hydrogen  sulphide  derived  from 
organic  sulphur.  These  grains  of  sulphide  are  so  small  that  they 
cannot  be  removed  from  the  coal  by  washing  unless  the  coal  has  been 
ground  to  fine  powder. 

1  Thiessen,  R.,  Finely  disseminated  sulphur  compounds  in  coal.  Trans.  Amer.  Inst. 
Min.  Met.  Eng.  Vol.  LXIII,  p.  913,  1920. 


ORGANIC   SULPHUR 


35 


The  most  common  sulphate  known  is  calcium  sulphate  or  gypsum 
(CaSO4.2H2O).  Sulphates  of  iron,  copper  and  magnesium  may  also 
occur  but  they  are  not  abundant.  These  salts  occur  as  a  result  of 
the  action  of  sulphuric  acid  on  carbonates  or  by  the  oxidation  of 
sulphides.  The  sulphuric  acid  may  result  from  the  oxidation  of 
iron  pyrite  as  in  the  following  equation :  FeS2  +  76  +  H20  =  FeSCX 
+  H2S04. 

Native  sulphur  occurs  only  as  the  result  of  extreme  oxidation  of 
some  of  the  minerals  mentioned  above  and  it  is  rare. 


I   » 


FIG.  6.     Photomicrograph  showing  finely  disseminated  pyrite  in  coal  (x  155). 
(Photo  by  R.  Thiessen.) 

Organic  sulphur.  —  It  has  for  many  years  been  recognized  that  a 
portion  of  the  sulphur  in  coal  must  exist  in  some  form  other  than 
the  mineral  sulphides  and  sulphates.  This  is  shown  by  the  fact  that 
in  some  coals  the  sulphur  does  not  exist  in  such  proportions  that  it 
can  be  combined  with  the  elements  necessary  to  form  these  mineral 
compounds.  Sulphur  which  gives  every  indication  of  being  com- 


36  THE   CHEMICAL  PROPERTIES  OF  COAL 

bined  in  organic  compounds  in  coal  has  been  found  running  from  0.5 
to  2  per  cent,  and  3  per  cent  is  reported  in  one  coal.  Thiessen  points 
out  that  there  is  sulphur  in  the  proteins  of  practically  all  plants  and 
in  addition  to  the  protein  sulphur  there  is  some  non-protein  sulphur 
in  most  of  them.  This  organic  sulphur  by  putrefaction  is  changed 
to  hydrogen  sulphide  (H2S)  which  can  precipitate  sulphides  of  the 
metals  from  their  soluble  salts.  The  plants  obtain  the  sulphur, 
which  they  assimilate  in  the  form  of  sulphates,  from  the  weathering 
of  sulphides  in  the  rocks  or  from  the  products  of  sulphur  bacteria, 
which  oxidize  hydrogen  sulphide  to  sulphuric  acid.  The  sulphuric 
acid  can  then  form  calcium,  magnesium  or  potassium  sulphates, 
which  are  assimilated  by  the  plants.  R.  Dawson  Hall  has  also  called 
attention  to  the  fact  that  many  coal  seams  contain  a  larger  proportion 
of  sulphur  than  the  rocks  lying  above  and  below  them,  indicating 
the  presence  of  organic  sulphur  compounds  in  coal.  He  early  sus- 
pected that  some  of  the  sulphur  in  pyrite  had  an  organic  origin. 

Phosphorous.  —  Like  sulphur,  phosphorous  is  an  important  con- 
stituent in  coal  which  is  to  be  used  in  making  coke  since  they  both 
enter  the  coke  to  at  least  some  degree.  Its  presence  in  the  coal  may 
be  due  to  solutions  formed  by  streams  running  over  rocks  which 
contain  calcium  phosphate  in  some  form  and  these  solutions  then 
precipitating  the  phosphate  in  the  swamps  where  the  coal  vegetation 
was  laid  down.  It  is  evident,  however,  that  a  certain  percentage  of 
the  phosphorous  is  derived  directly  from  the  vegetation  which  produces 
the  coal.  In  a  study  of  the  origin  and  distribution  of  phosphorous 
in  bituminous  and  cannel  coals  Carnot1  has  found  that  certain  parts 
of  plants,  especially  the  spores,  contain  considerable  phosphorous. 
In  a  series  of  analyses  he  found  in  the  Grande  Couche,  a  thick  seam 
at  Commentry,  0.00163  per  cent  of  phosphorous;  in  the  coal  of  Fer- 
rieres  0.01385  per  cent  and  in  anthracite  0.01467  per  cent  of  phos- 
phorous. In  several  stems  of  typical  Coal  Measure  plants  changed 
to  coal  he  found  from  a  trace  to  0.007  per  cent  phosphorous.  Various 
cannels  from  England  and  central  France  were  found  to  contain 
considerably  more  of  this  element  than  the  other  coals,  the  percentage 
varying  from  a  trace  to  0.028.  Several  bogheads  gave  0.019  to  0.0627 
per  cent. 

1  Carnot,  Ad.,  Sur  Porigine  et  la  distribution  du  phosphore  dans  la  houille  et  le  cannel 
coal.  Compt.  Rend.,  Vol.  99,  pp.  154-156,  1884. 


CALCIUM,   MAGNESIUM   AND  IRON  37 

For  comparison  the  spores  of  several  modern  types  of  ferns  related 
to  the  Carboniferous  plants  were  analysed  and  they  contained  from 
0.078  to  0.228  per  cent  of  phosphorous  compared  with  0.009  to  o.oio 
per  cent  for  the  body  of  the  fern.  The  Ceratizamia  mexicana  yielded 
0.28857  Per  cent  phosphorous  from  the  pollen  grains  and  0.11899  Per 
cent  from  the  envelopes  which  had  become  fairly  well  separated  from 
the  pollen  grains.  Mineral  charcoal  appears  to  be  higher  in  phos- 
phorous than  the  coal  associated  with  it  because  during  the  change 
from  coal  to  mineral  charcoal  the  phosphorous  remained  while  vola- 
tile constituents  were  lost,  thus  increasing  the  proportion  of  the  former. 

The  alkalies  and  chlorine.  —  Sodium  chloride  and  other  alkaline 
salts  may  be  carried  into  the  coal  in  saline  solutions  which  have 
been  derived  from  the  surrounding  rocks.  The  alkalies  are  derived 
chiefly  from  the  feldspars  and  related  minerals  and  they  are  set  free 
by  weathering  of  these  minerals.  The  chlorine  comes  from  plants 
and  from  igneous  rocks. 

Silica.  —  This  compound  enters  the  ash  of  the  coal  and  is  derived 
chiefly  from  mineral  matter  deposited  in  the  swamp  by  wind  and 
water  both  as  mechanical  sediment  and  in  solution.  It  is,  however, 
derived  partly  from  such  plants  as  the  horsetails  which  may  contain 
upwards  of  12  per  cent  of  it  in  their  stems. 

Calcium,  magnesium  and  iron.  —  All  three  of  these  elements  may 
be  carried  in  solution  as  carbonates  in  the  presence  of  carbon  dioxide. 
They  may  also  be  carried  as  sulphates  and  in  small  amounts  as  chlor- 
ides. The  iron  in  the  form  of  sulphate  or  chloride  on  coming  in  con- 
tact with  a  soluble  salt,  such  as  a  salt  of  calcium,  would  normally 
be  thrown  down  as  the  hydrous  oxide  unless  there  were  an  excess 
of  carbon  dioxide  present  to  prevent  oxidation  in  which  case  iron 
carbonate  might  be  precipitated  instead  of  the  oxide.  The  presence 
of  so  much  iron  carbonate  or  " black  band"  associated  with  the 
coal  deposits  in  parts  of  America  and  England  is  explained 
by  assuming  that  the  carbon  dioxide,  furnished  by  decomposing 
vegetation,  caused  the  iron  to  be  precipitated  as  the  carbonate  (sider- 
ite)  rather  than  as  the  more  commonly  occurring  hydrous  oxide. 

In  addition  to  the  elements  mentioned  there  may  be  found  in  coal 
ash,  traces  of  gold,  silver,  zinc,  lead,  copper,  titanium,  vanadium, 
manganese  and  a  vast  number  of  other  elements  of  no  particular 
economic  importance  but  of  some  scientific  interest.  Of  these  ele- 


THE   CHEMICAL  PROPERTIES  OF   COAL 


ments  zinc  has  been  found  in  wood,  and  manganese  occurs  up  to 
25.53  Per  cent  as  Mn3O4  in  the  ash  from  leaves  of  Norway  spruce,  and 
41.23  per  cent  in  the  ash  of  the  bark.  Some  Hawaiian  pineapples 
show  1.15  to  2.12  per  cent  Mn3O4.1  It  is  thus  evident  that  most  of 
the  elements  have  been  derived  in  part  directly  from  the  vegetation 
and  in  part  from  solutions  carried  into  the  swamps. 

The  following  table2  illustrates  the  composition  of  the  ash  from 
several  types  of  trees  and  it  shows  that  at  least  small  percentages 
of  most  of  the  elements  may  be  supplied  to  the  coal  from  the  vegetal 
matter  which  goes  to  form  it.  Some  elements  seem  to  be  entirely 
lacking  in  the  ash  of  the  common  plants,  while  others  are  extremely 
rare.  For  example,  molybdenum  and  caesium  are  lacking  while 

ANALYSES  OF  ASH  FROM  TREES 
(Dried  at  105°  in  oven) 


Birch  Leaves 
Per  cent 

Birch  Stems 
Per  cent 

Oak  Leaves 
Per  cent 

Oak  Stems 
Per  cent 

Pine    Needles 
Per  cent 

Pine    Stems 
Per  cent 

SiO2 

0.050 

0.030 

O.222 

0.024 

0.170 

o  .014 

TiO2  

Trace 

NF. 

Trace 

Trace 

0  .  OOOI 

O.OOI 

A1203.... 

0.24 

N.F. 

0.038 

0.070 

0-253 

0.090 

Fe203  .  .  . 

0.29 

0.015 

0.023 

O.O2O 

O.O2O 

0.016 

MnO.... 

0.655 

0.0098 

0.160 

0.0393 

0.0596 

O.OII 

Cr,O6.... 

N  F. 

N.F. 

Trace 

N.F. 

Trace 

N.F. 

V206  

N.F. 

N.F. 

N.F. 

N.F. 

Trace 

N.F. 

MoO2  .  .  . 

N.F. 

N.F. 

N.F. 

N.F. 

N.F. 

N.F. 

CaO  

i-4S 

0.440 

1.14 

1-25 

o  320 

0.240 

BaO  

O.OI2 

0.005 

0.015 

O.O20 

0.005 

0.007 

SrO  

0.006 

0.004 

0.013 

0.023 

0.003 

0.004 

MgO.... 

0-55 

0.170 

0.72 

0.18 

0.210 

0.130 

K2O  

i-99 

0.58 

0.91 

0.34 

O.gi 

0.30 

Na20.... 

O.IO 

0.13 

0.13 

0.15 

O.O7 

0.07 

Li2O    ... 

0.000047 

0.00003 

0.00015 

o  .  000003 

O.OOOO6 

0  .  OOOI 

Rb2O.... 

O.OOI 

0.0003 

O.OOOOI2 

0.0015 

O.OOOI5 

N.F. 

CS20.  ... 

N.F. 

N.F. 

N.F. 

N.F. 

N.F. 

N.F. 

P205  .... 

i  .10 

0-33 

0.261 

0.274 

0.27 

0.075 

SO3  

o-35 

0.16 

0-35 

0.16 

0.42 

0.14 

Cl  

0.12 

0.04 

0.06 

0.05 

O.II 

0.05 

H2O..... 

8.68 

8.26 

7-74 

6.68 

7.2 

8.4 

Mineral 

constitu- 

ents by 

addition 

5-8 

4.0 

4.0 

2.6 

2.8 

i.i 

1  Kelley,  W.  P.,  Manganese  in  some  of  its  relations  to  the  growth  of  pineapples.     Jour. 
Ind.  &  Eng.  Chem.,  Vol.  I,  p.  533,  1909. 

2  Robinson,  W.  O.,  Stemkoenig,  L.  A.,  and  Miller,  C.  F.,  The  relation  of  some  of  the 
rarer  elements  in  soils  and  plants.    U.  S.  Dept.  Agr.,  Bull.  No.  600,  Dec.  10,  1917. 


CALCIUM,   MAGNESIUM   AND   IRON  39 

chromium  and  vanadium  are  very  rare.  It  is  evident  that  the  high 
percentage  of  vanadium  in  the  ash  analysis  quoted  below  is  due 
entirely  to  some  external  source. 

An  analysis  of  ash  from  coal  near  the  town  of  San  Raphael  in  the 
province  of  Mendozza,  Argentina,  gave  the  following  results: 1 

Soluble  in  Acids  Percent  Insoluble  in  Acids  Percent 

Vanadic  acid 38 . 5          SiO2 13.6 

H2SO4 12.  i  A12O3 5.5 

P2O5 0.8          Fe2O3 9.4 

Fe2O3 4.1          MgO 0.9 

A12O3 4.0 

CaO 8.44 

K2O i. 80 

This  coal  contained  0.24  per  cent  of  vanadic  acid  and  this  constitu- 
ent was  no  doubt  injected  into  the  coal  by  solutions  which  percolated 
through  the.  seam  and  which  may  have  been  derived  from  igneous 
sources.  Igneous  rocks  are  the  source  of  most  of  such  rare  constit- 
uents in  coal. 

1  Mourlot,  A.,  Analyse  de  la  houille  vanadifere.  Compt.  Rend.,  Vol.  117,  pp.  546- 
548,  1893. 


CHAPTER  III 
CHEMICAL   ANALYSIS   OF   COAL 

Introduction 

The  analyzing  of  coal  has  long  been  recognized  as  the  best  laboratory 
means  of  determining  its  commercial  qualities.  Much  attention, 
therefore,  has  been  paid  by  chemists,  geologists,  and  mining  men, 
to  the  various  methods  for  obtaining  samples  and  making  analyses. 
To  be  of  any  real  value  for  purposes  of  comparison  with  other  coals 
or  as  a  means  of  determining  the  commercial  qualities  of  a  seam  the 
coal  analysed  must  be  selected  from  the  mine  according  to  some 
definite  scheme.  The  uninitiated  person  invariably  pays  too  little 
attention  to  sampling  and  he  very  often  picks  out  the  best  appearing 
coal,  thus  deceiving  not  only  his  customers  but  himself  regarding  the 
quality  of  the  coal  which  is  to  be  analysed.  Too  much  attention 
cannot  be  paid  to  the  selection  of  samples  which  properly  represent 
the  average  composition  of  a  coal  seam  or  a  shipment  of  coal. 

Sampling   for   Analysis 

The  importance  of  a  standard  method.  —  Different  companies  or 
institutions  may  have  their  own  methods  of  sampling,  but  it  is  de- 
sirable that  some  uniform  system  be  adopted  for  sampling  coal  in 
all  countries  in  order  that  the  analyses  made  from  the  samples  may 
be  available  for  comparative  purposes.  Much  care  has  been  taken 
to  standardize  methods  of  analysis  but  much  less  attention  has  been 
paid  to  standardizing  methods  of  sampling.  When  a  sample  is 
selected  from  a  seam  it  should  be  taken  in  such  a  way  that  it  will 
represent  the  coal  which  will  be  mined.  If  a  certain  portion  of  the 
parting  is  included  in  mining,  this  should  also  be  included  in  the 
sample.  A  standard  of  size  for  the  material  selected  is  also  of  im- 
portance because  the  manner  in  which  the  portions  of  the  seam 
high  in  ash  or  low  in  ash  break  down  on  crushing  will  vary  greatly. 
This  is  owing  to  the  varying  character  of  the  material  constituting 
bony  streaks  in  the  coal.  In  some  places  these  may  be  sandy  and  in 
others  argillaceous.  An  analysis  of  the  finely  powdered  material 

40 


THE  IMPORTANCE   OF  A   STANDARD  METHOD  41 

may  differ  distinctly  from  the  lumpy  portion,  and  standard  crushing 
and  screening  are  therefore  essential.  The  portion  of  the  seam  selec- 
ted is  a  factor  of  importance  because  weathered  coals  differ  in  com- 
position, heating  value,  and  coking  qualities  from  the  unweathered 
coal  of  the  same  seam  owing  to  the  effects  of  oxidation.  The  nature 
of  the  roof  and  floor  of  the  seam  has  an  important  bearing  on  the 
probable  weathered  condition  and  in  many  places  on  the  sulphur 
content.  Care  should  be  taken,  therefore,  to  observe  faulted  zones 
and  other  disturbed  areas.  Examples  are  known  where  the  coal 
near  the  outcrop  is  higher  in  sulphur  than  that  some  distance  under- 
ground owing  to  the  fact  that,  where  the  roof  is  fractured  as  a  result 
of  weathering,  sulphur  compounds  have  been  carried  into  the  coal 
from  overlying  pyrite-bearing  rocks.  The  writer  knows  of  one  case 
where  the  decision  to  purchase  an  important  property  on  which  the 
coal  was  regarded  as  a  high-sulphur  type  was  based  entirely  on  the 
consideration  of  this  phenomenon  and  the  deal  turned  out  very  suc- 
cessfully. In  some  mines  there  is  much  more  sulphur  in  the  "rolls" 
under  the  seam  than  in  the  adjacent  rocks  and  if  water  works  through 
fractures  in  these  rolls  the  sulphur  content  may  be  increased  in  the 
coal  adjacent  to  them. 

After  the  coal  is  obtained  from  the  mine,  car,  or  stock  pile,  care 
should  be  taken  to  see  that  if  it  is  not  analysed  at  once  it  is  kept  in 
air-tight  receptacles  in  order  that  it  may  not  lose  or  gain  moisture, 
lose  gas  or  become  oxidized.  It  is  well  known  that  coals  lose  a  large 
amount  of  methane  on  exposure  to  the  atmosphere  and  take  up  oxy- 
gen rapidly,  especially  just  after  removal  from  the  seam,  unless  they 
are  carefully  sealed.  The  altitude  at  which  a  sample  is  exposed  to 
the  air  also  has  a  bearing  on  its  composition  since  a  marked  change 
in  barometric  conditions  will  affect  the  rate  of  evaporation  of  moisture 
and  the  escape  of  gases. 

United  States  Bureau  of  Mines  and  Geological  Survey  mine  samp- 
ling methods.  —  In  proceeding  to  sample  a  mine  it  is  well  to  procure 
a  map  if  possible,  so  that  the  location  where  each  sample  is  taken 
may  be  properly  fixed.  The  number  of  samples  to  be  taken  will 
vary  a  great  deal  with  the  uniformity  of  the  coal  in  a  seam  but  about 
four  samples  for  a  daily  production  of  200  tons  or  less,  with  an  extra 
sample  for  each  additional  200  tons  mined  per  diem,  is  considered 
sufficient. 


42  CHEMICAL  ANALYSIS  OF  COAL 

In  taking  the  sample  the  United  States  Geological  Survey  and  the 
Bureau  of  Mines1  recommend  that  a  space  5  feet  in  width  be  cleared 
of  dirt  and  powder  from  top  to  bottom  of  the  seam.  Down  the 
center  of  this  cleared  space  a  zone  i  foot  wide  is  cut  to  a  depth  of  at 
least  i  inch,  in  order  to  get  perfectly  clean  coal  behind  that  removed. 
A  cut  is  then  made  up  the  center  of  this  zone  to  a  depth  of  2  inches 
and  a  width  of  6  inches  or,  if  the  coal  be  soft,  to  a  depth  of  3  inches 
and  a  width  of  4  inches.  There  should  thus  be  obtained  not  less 
than  5  to  6  pounds  of  coal  for  each  foot  thickness  of  the  seam  and 
this  should  include,  as  nearly  as  possible,  all  bony  coal  retained  in 
mining  operations,  and  it  should  exclude  all  partings  discarded  in 
mining.  It  is  suggested  that  in  most  places  partings  over  f  inch 
thick,  and  sulphur  balls,  or  other  impurities,  more  than  2  inches  in 
maximum  diameter  and  -|  inch  thick  be  omitted  from  the  sample. 

The  sample  taken  as  described  above  is  collected  on  a  collecting 
cloth  and  then  screened.  The  lumps  are  broken  in  a  mortar  and  all 
passed  through  a  ^-inch  or  f-inch  screen.  The  sample  is  thoroughly 
mixed  with  the  coarser  materials  evenly  distributed.  It  is  then 
quartered  and  after  remixing,  it  is  requartered,  if  it  be  still  too  large 
for  convenient  handling.  The  mixing  complete,  the  sample  is  placed 
in  a  can,  the  top  screwed  on  and  sealed  with  adhesive  tape.  The 
can  is  carefully  labeled  with  the  name  of  the  collector,  the  location, 
the  date,  and  all  other  information  which  might  be  of  service  when 
the  analysis  is  prepared.  The  government  bureaus  have  prepared 
very  elaborate  blank  forms,  which  are  filled  out  and  shipped  with 
the  cans. 

Equipment  for  mine  sampling.  —  As  equipment  for  the  special 
work  of  sampling,  the  following  materials  and  tools  have  been  sug- 
gested: A  portable  mortar  with  sides  5  inches  high  and  having  a 
capacity  of  500  cubic  inches;  a  pestle  consisting  of  a  steel  head, 
i  inch  thick  and  3  to  4  inches  long;  a  good  spring  balance  of  50  pounds 
capacity  graduated  to  ^  pound;  a  galvanized  iron  wire  screen  of 
f-inch  mesh  and  provided  with  a  wooden  frame;  a  galvanized  sheet- 

1  Holmes,  J.  A.,  The  sampling  of  coal  in  the  mine.  U.  S.  Bur.  of  Mines  Tech.  Paper 
I,  191 1 ;  Campbell,  M.  R.,  The  commercial  value  of  coal-mine  sampling.  Trans.  Amer. 
Inst.  of  Mng.  Eng.,  Vol.  36,  p.  341,  1906;  The  value  of  coal-mine  sampling.  Econ. 
Geol.  Vol.  2,  p.  48,  1907;  also  Parr,  S.  W.,  Chemical  study  of  Illinois  coals.  Illinois 
Coal  Mining  Investigations.  State  Geol.  Survey,  Bull.  3,  1916. 


SAMPLING  WAGON,   CAR,  OR  CARGO  LOTS  43 

iron  scoop  8  inches  long,  2  inches  deep  and  ii  inches  wide,  but  a 
trowel  or  shingle  will  serve  in  place  of  this;  a  stiff  brush;  a  2O-foot 
waterproof  measuring  tape;  a  sampling  can  about  9  inches  deep 
by  3  inches  in  diameter  made  of  No.  27  galvanized  iron  which  is 
crimped  and  soldered  to  make  it  strong  and  air-tight;  adhesive  tape; 
a  pick;  and  a  shovel. 

Sampling  wagon,  car,  or  cargo  lots.  —  In  sampling  wagon-loads, 
carloads,  or  cargo  lots  of  coal  care  should  be  taken  to  collect  a  repre- 
sentative sample  by  choosing  shovelfuls  from  different  parts  of  the 
load  or  pile  and  including  an  average  amount  of  impurities.  If  the 
coal  be  in  coarse  fragments,  a  larger  sample  should  be  collected  than 
if  it  be  finely  broken.  About  1000  pounds  should  be  taken  as  a  gross 
sample  for  carload  or  cargo  lots  and  this  should  be  increased  to  at 
least  1500  pounds  if  the  coal  contains  much  impurity  in  coarse  frag- 
ments. It  has  been  found  that  the  analysis  of  a  large  gross  sample 
comes  closer  to  the  average  for  the  lot  than  a  small  one,  up  to  a  certain 
limit,  above  which  there  is  no  advantage  in  increasing  the  size  of 
the  gross  sample.1 

The  looo-pound  sample  may  be  crushed  so  as  to  pass  a  i-inch 
screen.  It  is  then  mixed,  halved,  by  quartering  method,  and  passed 
through  a  f-inch  screen.  This  process  is  continued  until  a  3o-pound 
sample  is  obtained  which  will  pass  a  T\-inch  screen.  After  thorough 
mixing  and  quartering  a  sample  weighing  5  pounds  is  taken  for  an- 
alysis. 

From  the  tests  of  various  coals  by  the  United  States  Geological 
Survey  and  Bureau  of  Mines  it  has  been  found  that  certain  differences 
exist  between  the  analyses  of  mine  samples  and  carload  lots  of  the 
same  coal.  These  differences  are  due  chiefly  to  oxidation  and  to 
the  changes  in  the  moisture  and  gas  content  while  exposed  to  the 
atmosphere  during  transportation.  The  following  statements  apply 
in  most  cases.  In  lignite  and  lignitic  coals  the  moisture  content  is 
greater  in  the  car  sample  than  in  that  taken  in  the  mine  and  the  de- 
crease in  calorific  value  may  amount  to  1.3  per  cent  in  the  moisture- 
free  and  ash-free  coal.  If  bituminous  coals  have  a  moisture  content 

1  Pope,  G.  S.,  Methods  of  sampling  delivered  coal.  U.  S.  Bur.  of  Mines,  Bulls.  63, 
1913  and  116,  1916;  Bailey,  E.  G.,  Accuracy  in  sampling  coal.  Jour.  Ind.  Eng.  Chem., 
Vol.  i,  p.  1612,  1909;  also  Parr,  S.  W.,  Purchase  and  sale  of  Illinois  coal  on  specification. 
111.  State  Geol.  Survey,  Bull.  29,  1914.  (Methods  of  Sampling.) 


44  CHEMICAL  ANALYSIS  OF  COAL 

of  over  5  per  cent  in  mine  samples  they  usually  lose  moisture  in  tran- 
sit but  they  also  lose  calorific  value  from  0.3  to  0.8  per  cent.  Those 
with  less  than  5  per  cent  usually  show  a  gain  in  moisture  up  to  about 
1.5  per  cent  and  the  change  in  calorific  value  amounts  to  a  very  small 
decrease.1 

Standard  method  of  sampling.  —  The  Joint  Committee  of  the 
American  Society  for  Testing  Materials  and  the  American  Chemical 
Society2  suggests  the  following  methods  for  sampling  and  the  method 
described  in  the  final  report  of  the  Committee  will  hereafter  be  known 
in  this  work  as  the  standard  method  of  sampling  and  analyzing  coal. 
It  is  insisted  that  the  method  outlined  should  be  used  in  obtaining 
a  sample  whether  it  is  taken  from  a  i-ton  lot  or  from  a  lot  containing 
hundreds  of  tons.  Also  if  this  method  is  adopted  in  a  contract  the 
following  provisions  shall  be  agreed  upon  (i)  Place  sampling  is  done, 
(2)  Approximate  size  of  sample  required  when  standard  conditions 
do  not  apply,  (3)  The  number  of  samples  to  be  taken  or  the  amount 
of  coal  to  be  represented  by  each  sample  when  the  standard  con- 
ditions (i.e.  those  outlined  below)  do  not  apply. 

For  the  determination  of  all  constituents  except  that  of  total 
moisture  the  following  regulations  are  observed  (i)  The  coal  is  sampled 
as  it  is  loaded  into  or  unloaded  from  conveyances  or  bins.  If  the 
coal  is  crushed  as  received  samples  may  be  taken  after  the  crushing. 
Samples  from  the  surfaces  of  piles  are  not  reliable.  (2)  For  taking 
samples  a  shovel  or  specially  designed  tool  capable  of  taking  equal 
portions  of  the  coal  shall  be  used.  For  slack  or  small  sizes  of  an- 
thracite increments  as  small  as  5  to  10  pounds  may  be  taken  but  for 
run-of-mine  or  lump  coal  10  to  30  pounds  may  be  taken.  (3)  The 
gross  sample  shall  be  not  less  than  1000  pounds  and  the  increments 
shall  be  so  regularly  and  systematically  collected  that  the  entire 
quantity  of  coal  shall  be  properly  represented  in  the  sample.  If 
the  fragments  are  small,  not  exceeding  f  inch  in  size  a  sample  of  500 
pounds  is  sufficient.  If  there  is  an  unusual  amount  of  slate  or  other 
impurities  or  if  the  fragments  are  unusually  large  1 500  pounds  should 

1  Campbell,  M.  R.,  Op.  cit.     Also  Fieldner,  A.  C.,  Notes  on  the  sampling  and  analysis 
of  coal.     U.  S.  Bur.  of  Mines,  Tech.  Paper  76,  1914.     For  detailed  descriptions  of  analyses 
see:    Methods  of  analyzing  coal  and  coke,  by  F.  M.  Stanton  and  A.  C.  Fieldner,  U.  S. 
Bur.  of  Mines,  Tech.  Paper  8,  1913. 

2  American  Society  for  Testing  Materials,  A.  S.  T.  M.  Standards,  (D  21-16),  1918, 
P-  673. 


STANDARD   METHOD   OF   SAMPLING  45 

be  taken.     The  following  table  shows  the  relation  of  the  sizes  of  the 
fragments  of  the  coal  to  the  weight  of  the  sample  taken.     (4)  A 

TABLE  A 


Weight  of  sample  to  be  divided. 
In  pounds 


Largest  size  of  coal  and  impurities  in  sample 
before  division.     In  inches 


1000  or  more 

500 

250 

125 
60 

30 


T\  or  4-mesh  screen 


gross  sample  shall  be  taken  for  each  500  tons  or  less,  or  in  larger 
tonnages  according  to  agreement.  (5)  The  gross  sample  shall  be 
systematically  crushed,  mixed  and  reduced  in  quantity  to  convenient 
size  for  transmittal  to  the  laboratory.  The  crushing  may  be  done 
by  hand  or  by  mechanical  means,  but  loss  and  addition  of  foreign 
matter  must  be  prevented.  (6)  The  progressive  reduction  of  the 
sample  to  the  various  quantities  and  sizes  mentioned  in  the  table 
above  shall  be  carried  out  in  the  following  way :  (a)  The  gross  sample 
is  reduced  to  250  pounds  by  the  alternate  shovel  method  observing 
the  requirements  for  relative  sizes  and  weights  in  Table  A,  and  div- 
iding the  coal  as  follows:  The  crushed  coal  is  shoveled  into  a  conical 
pile  by  placing  each  shovelful  on  top  of  the  one  previously  deposited 
and  then  piling  the  coal  in  this  pile  in  a  long  pile  as  wide  as  the  shovel 
and  5  to  10  feet  long.  This  long  pile  is  made  by  spreading  each  shovel- 
ful out  for  the  full  width  and  length  of  the  pile  with  alternate  shovel- 
fuls spread  from  opposite  ends  of  the  pile.  The  pile  is  flattened  from 
time  to  time.  Half  of  this  pile  is  discarded  by  beginning  at  the  end 
of  the  pile  and  taking  shovelfuls  side  by  side  and  one  after  the  other 
along  the  side  of  the  pile.  These  alternate  shovelfuls  are  placed  in 
two  different  piles  and  the  operation  continued  until  the  long  pile 
is  completely  encompassed  and  practically  all  the  coal  divided  be- 
tween the  two  piles,  (b)  The  sample  now  reduced  to  about  250 
pounds  is  quartered,  observing  the  relations  outlined  in  Table  A. 
Quantities  of  125  to  250  pounds  are  coned  and  re-coned  while  smaller 
samples  are  placed  on  a  cloth  about  6  by  8  feet  and  mixed  by  raising 
first  one  end  and  then  the  other  so  as  to  roll  the  coal  back  and  forth. 


46  CHEMICAL  ANALYSIS  OF  COAL 

By  gathering  the  four  corners  of  the  cloth  a  conical  pile  is  formed  and 
then  quartered  by  first  flattening  down  the  apex  uniformly  and  care- 
fully and  then  dividing  the  pile  into  quarters  so  that  the  dividing 
lines  intersect  at  a  point  beneath  the  apex  of  the  original  cone.  The 
alternate  quarters  are  discarded  and  the  process  described  above  is 
repeated  until  a  sample  of  about  30  pounds  is  secured,  (c)  The 
3o-pound  sample  is  crushed  to  T\  inch  or  4-mesh  size,  mixed,  flattened 
and  quartered.  The  laboratory  samples  shall  include  all  of  one  of 
the  quarters  or  all  of  two  opposite  quarters  if  required  and  it  is  im- 
mediately placed  in  a  container  designed  for  this  purpose  and  sealed. 
For  the  total  moisture  determination  a  special  sample  of  about 
100  pounds  weight  is  made  up  by  placing  in  a  waterproof  receptacle 
equal  parts  of  freshly  taken  increments  of  the  standard  gross  sample. 
This  sample  shall  be  rapidly  crushed  and  reduced  mechanically  or  by 
hand  to  about  5  pounds.  This  smaller  sample  is  at  once  sealed  air- 
tight in  a  container  and  sent  immediately  to  the  laboratory.  The 
standard  gross  sample  shall  not  be  used  in  place  of  this  special  moisture 
sample  unless  equally  representative  results  can  be  obtained  from  it. 

Preparation  of  Laboratory  Samples  by  Standard  Method1 
Apparatus.  —  (a)  Jaw  crusher  for  crushing  coarse  samples  to  pass 
a  4-mesh  sieve,  (b)  Roll  crusher  or  coffee-mill  type  of  grinder  for 
reducing  samples  to  2o-mesh.  This  mill  should  be  entirely  enclosed 
and  have  an  enclosed  hopper  capable  of  holding  10  pounds  of  coal. 
(c)  Abbe  Ball  Mill,  Planetary  Disk  Crusher,  Chrome-steel  bucking 
board  or  any  satisfactory  form  of  pulverizer  for  reducing  the  2o-mesh 
material  to  6o-mesh.  For  the  ball  mill  the  porcelain  jars  should  be 
approximately  9  inches  in  diameter  and  10  inches  high.  The  flint 
pebbles  should  be  smooth  and  well-rounded,  (d)  Large  Riffle  sam- 
pler with  -j-  or  | -inch  divisions  for  reducing  the  4-mesh  sample  to 
10  pounds,  (e)  Small  Riffle  sampler  with  J-  or  f-inch  division  for 
dividing  down  the  20-mesh  and  6o-mesh  material  to  a  laboratory 
sample.  (/)  Eight-inch,  6o-mesh  sieve  with  cover  and  receiver. 
(g)  Galvanized  iron  pans,  18  by  18  by  ij  inches  deep  for  air-drying 
wet  samples,  (h)  Balance  or  solution  scale  for  weighing  the  pans 

1  Final  report  on  coal  analysis  of  the  Joint  Committee  of  the  American  Society  for 
Testing  Materials  and  the  American  Chemical  Society.  Jour.  Ind.  and  Eng.  Chem., 
Vol.  9,  No.  i,  p.  100,  1917.  Also  American  Society  for  Testing  Materials,  A.  S.  T.  M. 
Standards  (D  22-16),  p.  679,  1918. 


METHOD  OF  SAMPLING  47 

and  samples.  (Required  capacity  5  kilograms  and  sensitive  to  0.5 
gram.)  (i)  Air-drying  oven  to  be  used  for  drying  wet  samples. 
Not  absolutely  necessary.  (Description  in  Bull.  No.  9,  Geol.  Survey 
of  Ohio,  p.  312.) 

Method  of  sampling.  —  There  are  two  methods,  the  choice  de- 
pending upon  whether  coal  appears  wet  or  dry. 

I.  When  coal  appears  dry  the  first  procedure  is  to  reduce  the  coal 
in  the  jaw  crusher  to  pass  a  4-mesh  sieve  and  reduce  the  sample  to 
10  pounds  weight,  on  the  larger  riffle  sampler.     (If  crushed  to  pass 
6-mesh  the  sample  may  be  reduced  to  5  pounds.)     The  lo-pound 
4-mesh  sample  is  ground  in  a  roll  crusher  or  coffee-mill  to  2O-mesh. 
From  various  parts  of  this  sample,  take  with  a  spoon,  without  sieving, 
a  composite  6o-gram  total-moisture  sample  which  should  be  placed 
directly  in  a  rubber-stoppered  bottle. 

Thoroughly  mix  the  main  portion  of  the  sample,  reduce  on  the 
smaller  riffle  sampler  to  about  120  grams  and  pulverize  to  6o-mesh 
by  suitable  grinder,  disregarding  loss  of  moisture.  After  passing 
6o-mesh  the  sample  is  mixed  and  reduced  to  60  grams  on  the  small 
riffle  sampler.  This  final  sample  is  transferred  to  a  4-oz.  rubber- 
stoppered  bottle.  Moisture  is  determined  on  both  the  6o-mesh  and 
20-mesh  samples.  The  following  computation  is  made:  The  analysis 
of  the  6o-mesh  coal  which  has  become  partly  air-dried  during  samp- 
ling is  computed  to  the  dry-coal  basis  by  dividing  each  result  by  i 
minus  its  content  of  moisture.  The  analysis  of  the  coal  "  as  received  " 
is  computed  from  the  dry-coal  analysis  by  multiplying  by  i  minus  the 
total  moisture  found  in  the  2o-mesh  sample. 

II.  When   coal   appears  wet   the   following  method  is   followed: 
The  sample  is  spread  on  tared  pans,  weighed  and  air-dried  at  room 
temperature,  or  in  the  special  drying  oven  previously  mentioned,  at 
10°  to  15°  C.  above  room  temperature.     It  is  weighed  again.     This 
drying  is  continued  until  the  loss  of  weight  is  not  more  than  o.i  per 
cent  per  hour.     The  sampling  is  then  completed  as  under  I  for  dry 
coal. 

The  following  computation  should  be  made:  Correct  the  moisture 
found  in  the  2O-mesh  air-dried  sample  to  total  moisture  "as  received" 
according  to  the  following  formula. 

loo  —  percentage  of  air-drying  loss  vx  f  r 

— X  (percentage   of   moisture  in 


100 


48  CHEMICAL  ANALYSIS   OF  COAL 

2o-mesh  coal)  +  (percentage  of  air-drying  loss)  =  (total  moisture 
"as  received")-  Compute  the  analysis  to  " dry-coal"  and  "as  re- 
ceived" bases  as  under  dry  coal,  using  for  the  "as  received"  compu- 
tations the  total  moisture  as  found  by  the  formula  in  place  of  the 
moisture  found  in  the  20-mesh  coal. 

Precautions:  Owing  to  the  fact  that  freshly  mined  or  wet  coal 
loses  moisture  rapidly  in  the  laboratory  the  sampling  operations  should 
be  carried  out  as  quickly  as  possible  between  the  time  of  opening  the 
container  and  the  securing  of  the  2o-mesh  sample  and  the  sample 
should  be  exposed  to  the  air  as  little  as  possible.  The  accuracy  of 
the  method  of  preparing  the  laboratory  samples  should  be  frequently 
checked  by  using  duplicate  samples  and  by  resampling  rejected  por- 
tions of  samples.  The  ash  in  two  samples  should  not  differ  more  than 
the  following  amounts  under  the  conditions  stated:  if  no  carbonates 
are  present  0.4  per  cent;  considerable  carbonates  and  pyrite  present 
0.7  per  cent;  coals  with  more  than  12  per  cent  ash,  containing  con- 
siderable carbonate  and  pyrite  i  .o  per  cent. 

English  method.  —  In  the  English  government  laboratories1  the 
coal  is  usually  received  in  the  laboratory  in  tins  such  as  biscuit  tins, 
enclosed  in  wooden  boxes,  each  sample  weighing  20  to  30  pounds. 
The  sample  is  passed  through  a  i-inch  sieve,  mixed  thoroughly, 
quartered  and  one-half  returned  to  the  tin.  The  other  half  is  crushed 
in  a  small  Marsden-Blake  crusher  and  by  quartering  reduced  to  about 
i  pound.  It  is  then  ground  in  a  closely  set  coffee-mill  and  divided 
into  two  parts,  one  of  which  is  placed  in  a  stoppered  bottle  and  sealed 
for  future  reference  purposes,  the  other  being  placed  in  a  similar  bottle 
for  analysis.  The  sample  taken  from  the  coffee-mill  is  used  for  tests 
on  moisture  and  volatile  matter  but  for  other  estimations  a  portion 
is  ground  to  pass  a  5o-mesh  sieve.  The  moisture  is  also  determined 
in  the  latter  portion  but  the  practice  of  determining  the  volatile  mat- 
ter in  this  portion  also,  has  been  discontinued  as  it  has  been  found 
that  the  results  differ  very  little  for  the  two  samples. 

The  Proximate  Analysis 

The  proximate  analysis  or  the  determination  of  moisture,  volatile 
matter,  fixed  carbon,  ash  and  sulphur  is  the  analysis  usually  made  for 
practical  purposes  since  it  is  much  more  readily  made  than  the  ulti- 
1  Pollard,  W.,  Memoirs  of  the  Geol.  Survey,  England  and  Wales,  p.  6,  1915. 


MOISTURE   DETERMINATION 


49 


mate  analysis  and  it  furnishes  most  of  the  data  necessary  for  the 
purpose  of  arriving  at  the  quality  of  the  coal.  From  it  the  grouping 
of  the  elements  in  the  form  most  closely  affecting  combustion  can  be 
determined. 

Moisture  determination  by  the  standard  method.  —  Apparatus: 
The  apparatus  recommended  consists  of  the  following  articles:  (i) 
Moisture  oven  so  constructed  as  to  provide  a  minimum  air  space  and  a 
uniform  temperature  in  all  parts  of  the  chamber.  The  air  in  the 
oven  must  be  renewed  2  to  4  times  every  minute  and  the  air  must  be 
dried  by  passing  it  through  sulphuric  acid.  (2)  Capsules  with  covers 
which  permit  the  determination  of  ash  in  the  same  sample.  Those 
recommended  are  the  Royal  Meissen  porcelain  capsule  No.  2,  J  inch 
deep  and  if  inches  in  diameter,  or  a  fused  silica  capsule  of  similar 
shape  with  a  well-fitting  flat  aluminum  cover.  Glass  capsules  with 
ground  glass  caps  may  also  be  used  and  they  should  be  as  shallow  as 
possible  consistent  with  conven- 
ient handling. 

Method:  (i)  For  determination 
of  moisture  in  the  6o-mesh  sample 
the  empty  capsules  are  heated 
under  the  conditions  at  which  the 
coal  is  to  be  dried,  then  covered 
and  cooled  over  concentrated 
sulphuric  acid  (sp.  gr.  1.84)  for 
thirty  minutes  and  weighed.  Ap- 
proximately i  gram  of  the  sample 
is  dipped  from  the  bottle  with  a 
spatula  and  placed  in  the  capsules 
which  are  immediately  closed  and 
weighed. 

The  covers  are  removed  and  the 
capsules  quickly  placed  in  a  pre- 
heated oven  (at  104  to  110°  C.)  through  which  passes  a  current  of 
air  dried  by  concentrated  sulphuric  acid.  The  oven  is  closed  at 
once  and  the  specimens  are  heated  for  one  hour.  The  oven  is  then 
opened,  the  capsules  quickly  covered,  and  cooled  in  a  desiccator  over 
concentrated  sulphuric  acid.  When  cool  they  are  weighed  and  the 
moisture  computed. 


FIG.  7.  —  Moisture  oven.     (After  Stan- 
ton  and  Fieldner,  U.  S.  Bureau  of 
Mines.     Tech.  Paper  8.) 


50  CHEMICAL  ANALYSIS  OF   COAL 

(2)  For  the  determination  of  moisture  in  the  2o-mesh  sample 
5-gram  samples  are  used  and  they  are  weighed  with  an  accuracy  of  2 
milligrams.  They  are  heated  for  one  and  a  half  hours,  otherwise 
the  procedure  is  the  same  as  that  described  above  for  the  6o-mesh 
sample. 

Notes:  The  permissible  differences  in  duplicate  determinations  are 
as  follows: 


Same  analyst 

Different  analysts 

Moisture  under  5  per  cent  
Moisture  over  5  per  cent 

o  .  2  per  cent 
o  3  per  cent 

0.3  per  cent 
o  <?  per  cent 

Determination  of  ash  by  the  standard  method.  —  The  ash  in  coal 
or  coke  is  a  non-combustible  mixture  consisting  of  silicates  of  the 
alkalies,  calcium,  magnesium,  iron,  and  titanium;  oxides  of  iron  and 
silicon;  carbonates  of  iron,  calcium  and  magnesium  which  may 
change  to  oxides  on  heating;  sulphates,  the  most  common  one  being 
that  of  calcium;  phosphates;  and  arsenides.  The  color  of  the  ash 
is  often  an  indication  of  its  composition,  as  a  pure  white  ash  generally 
indicates  the  absence  of  iron  and  a  red  ash  its  presence,  although  lime 
may  counteract  the  color  of  the  iron  and  a  cream-colored  ash  may 
indicate  the  presence  of  both  lime  and  iron.  Effervescence  with 
acid  shows  that  carbonates  are  present. 

Apparatus:  (i)  A  gas  or  electric  muffle  furnace.  It  should  have  a 
good  air  circulation  and  be  capable  of  maintaining  a  regular  tempera- 
ture between  700°  and  750°  C.  (2)  Porcelain  capsules.  Those  rec- 
ommended are  the  Royal  Meissen  No.  2,  J  inch  deep  and  if  inches 
in  diameter. 

Method:  The  procelain  capsules,  containing  the  dried  coal  from 
the  moisture  determination,  are  placed  in  a  cold  muffle  furnace  or  on 
the  hearth  at  a  low  temperature  and  gradually  heated  to  redness  at 
such  a  rate  as  to  avoid  loss  of  particles  of  the  sample  from  the  rapid 
expulsion  of  the  volatile  matter.  The  ignition  is  finished  when  con- 
stant weight  is  obtained  (o.ooi  gram)  at  a  temperature  between  700 
and  750°  C.  The  capsules  are  cooled  in  a  desiccator  and  weighed. 

Notes  and  precautions:  The  permissible  differences  in  duplicate 
determinations  are  as  follows: 


DETERMINATION  OF  ASH  51 


Same  analyst 

Different  analysts 

No  carbonates  present  

o  .  2  per  cent 

o  .  3  per  cent 

Carbonates  present  

0.3        " 

o.<>        " 

Coal  with  more  than  12  per 
cent  ash  containing  carbon- 
ates and  pyrite 

0.5        " 

I    0 

Before  the  capsules  are  placed  in  the  muffle  for  ignition  to  constant 
weight  the  ash  should  be  stirred  with  a  platinum  or  nichrome  wire. 
Stirring  once  or  twice  before  the  first  weighing  hastens  complete 
ignition. 

The  result  obtained  as  above  is  "  uncorrected "  ash.  The  mineral 
matter  in  the  ash  differs  materially  from  the  actual  minerals  in  the 
coal. 

Other  notes  and  methods:  Some  analysts  have  used  a  platinum 
crucible  but  this  is  not  suitable  for  this  purpose  because,  as  stated 
by  Carnot,  if  a  platinum  crucible  which  contains  carbon  is  heated 
for  some  time  a  deposit  of  carbon  and  platinum  dust  may  be  made 
which  affects  the  weight  of  the  ash.  A  platinum  crucible  should 
never  be  used  with  coal  containing  pyrites.  A  coal  high  in  pyrites 
is  liable  to  cause  more  trouble  if  heated  too  rapidly  than  one  without 
this  mineral. 

For  the  rapid  determination  of  ash  in  coal,  in  the  field,  Lesher  has 
designed  an  apparatus  for  the  use  of  the  geologists  of  the  United 
States  Geological  Survey.  By  means  of  it  the  ash  can  usually  be 
determined  within  2  per  cent  of  the  figures  obtained  by  laboratory 
methods.1 

There  are  often  considerable  errors  in  the  result  obtained  in  the 
analyses  of  ash  owing  to  the  fact  that  the  carbonates  may  change 
to  oxides  or  to  sulphates,  depending  upon  certain  conditions.  If  a 
carbonate  changes  to  an  oxide  during  combustion  the  carbon  dioxide 
driven  off  escapes  and  is  lost  to  the  ash  while  its  carbon  is  computed 
with  the  carbon,  making  it  too  high.  This  carbon  is  not  in  a  com- 
bustible form  and  therefore  does  not  add  to  the  value  of  the  coal. 
It  will  be  seen  that  the  oxygen  is  also  affected  by  the  error.  Although 
these  errors  in  the  determination  of  ash,  carbon  and  oxygen,  are  not 

1  Lesher,  C.  E.,  Field  apparatus  for  determining  ash  in  coal.  U.  S.  Geol.  Survey, 
Bull.  62I-A,  1915. 


CHEMICAL  ANALYSIS  OF   COAL 


considered  in  technical  operation,  where  they  are  large  they  have  an 
important  bearing  on  correct  methods  of  analysis  and  on  the  heating 
value  of  the  coal.  They  have  been  fully  discussed  by  a  number  of 
writers  and  formulae  have  been  suggested  for  their  correction.1 

After  the  ash  has  been  obtained  from  the  coal,  it  may  be  analyzed 
in  much  the  same  way  as  any  other  inorganic  mixture. 

The  following  figures  show  the  composition  of  some  typical  coal 
ashes: 


I. 

Per  cent 

II. 
Per  cent 

SiO2 

15.2-64.7 
8.6-34.6 
3.8-19.0 
I  .O-lS.I 
0.4-10.0 
0.3-   2.9 
o-i-  5-3 

-    2.6 

Included  with  A12O3 
0.1-26.9 

45  .  24-50  .  23 
23-43-33-28 
5.50-14.68 
2.76-  8.52 
0.78-  2.88 
-3-83 

A12O3 

Fe2O3   .  .  . 

CaO  

MgO  

K2O  

Na2O  

TiO2 

P2O5  

0.26-  1.85 
0-96-  3.92 

SO3  

Temperature  of  fusio 

n  

ii5o°-i5oo°  C. 

I.  =  Variations  in  composition  shown  in  9  analyses  of  ash  from  various  types 

of  coals.     Quoted  by  Fieldner,  Op.  cit.,  p.  29. 

II.  =  Variations  in  composition  shown  in  4  analyses  quoted  by  Carnot,  Op.  cit., 
p.  212. 

The  fusibility  of  the  ash  of  coal  is  very  variable.  Like  that  of  clay 
it  is  lowered  by  the  presence  of  such  constituents  as  lime,  iron,  al- 
kalies and  magnesia.  The  temperature  of  fusibility  is  determined 
by  use  of  seger  cones  or  the  pyrometer.  The  ash  itself  may  be  molded 
into  a  pyramid  and  the  temperature  at  which  the  pyramid  bends  over 
to  its  base  is  considered  the  point  of  fusibility.  The  more  readily  the 
ash  fuses  the  greater  the  difficulty  arising  from  clinkers  in  the  fur- 
nace. The  formation  of  clinkers  can,  however,  be  controlled  to  a 
considerable  extent  by  careful  firing. 

A  list  of  analyses  and  the  softening  temperatures  of  a  large  number 
of  western  coals  is  as  follows.2 

1  Parr,  S.  W.,  Determination  of  ash.     Jour.  Ind.  and  Eng.  Chem.,  Vol.  5,  p.  523,  1913. 
Fieldner,  A.  C.,  Op.  cit.,  p.  27.     Pollard,  Op.  cit.,  p.  40. 

2  Selvig,  W.  A.,  Lenhart,  L.  R.,  and  Fieldner,  A.  C.,  Temperatures  at  which  ash  from 
western  coals  fuses  to  a  sphere.    Coal  Age,  Vol.  18,  No.  14,  p.  677,  1920. 


DETERMINATION  OF  PHOSPHOROUS   IN  ASH  53 

Average  for  samples  tested: 

Alaska 2040-3010°  F.         Nevada 2190-2480°  F. 

California 2220-2340  New  Mexico 2000-3000  + 

Idaho 1950-2640  Oregon 2060-2890 

Montana 1930-2790  Utah 2040-2880 

Washington 1870-3000  -f 

Determination  of  phosphorous  in  ash  by  the  standard  method.  —  I. 

First  method:  The  following  method  is  to  cover  all  cases:  To  the 
ash  from  5  grams  of  coal  in  a  platinum  capsule  there  is  added  10  c.c. 
of  HNO3  and  3  to  5  c.c.  of  HF.  The  liquid  is  evaporated  and  the 
residue  fused  with  3  grams  of  Na2CO3.  If  unburned  carbon  is  present 
in  the  ash  0.2  grams  of  NaNO3  is  mixed  with  the  carbonate.  The 
melt  is  leached  with  water  and  the  solution  filtered.  The  residue  is 
then  ignited,  fused  with  Na2CO3  alone,  the  melt  leached  and  the 
solution  filtered.  The  filtrates  are  combined,  held  in  a  flask,  acidified 
with  HNOa  and  concentrated  to  a  volume  of  100  c.c.  To  this  solution 
raised  to  85°  C.  there  is  added  50  c.c.  of  molybdate  solution  and  the 
flask  is  shaken  for  ten  minutes.  If  the  precipitate  does  not  form 
promptly  and  settle  quickly,  enough  NH4NO3  is  added  to  cause  it 
to  do  so.  The  precipitate  is  washed  six  times  or  until  free  from  acid, 
with  a  2  per  cent  solution  of  KNO3,  then  returned  to  the  flask  and 
titrated  with  standard  NaOH  solution.  The  alkali  solution  may  be 
made  equal  to  0.00025  gram  phosphorous  per  cubic  centimeter,  or 
0.005  Per  cent  f°r  a  5-£ram  sample  of  coal  and  is  0.995  °f  one-fifth 
normal.  Or  the  phosphorous  in  the  precipitate  is  determined  by 
reduction  and  titration  of  the  molybdenum  with  permanganate. 

The  advantage  in  the  use  of  HF  in  the  initial  attack  on  the  ash 
lies  in  the  removal  of  silica.  Fusion  with  alkali  carbonate  is  necessary 
for  the  elimination  of  titanium,  which  if  present  and  not  removed  will 
contaminate  the  phospho-molybdate  and  is  said  to  sometimes  retard 
its  precipitation. 

II.  Second  method:  Where  titanium  is  so  low  as  to  offer  no  ob- 
jection, the  ash  is  decomposed  in  the  same  manner  as  in  the  first 
method  described  above,  but  evaporation  is  carried  only  to  a  volume 
of  about  5  c.c.  The  solution  is  diluted  with  water  to  30  c.c.,  boiled 
and  filtered.  If  the  washings  are  turbid  they  are  again  passed  through 
the  filter. 

The  residue  is  ignited  in  a  platinum  crucible,  fused  with  a  little 


54 


CHEMICAL  ANALYSIS  OF  COAL 


Na2CO3,  and  the  melt  is  dissolved  in  HNO3.  If  the  solution  is  clear  it 
is  added  to  the  main  one  but  if  not  clear  it  is  filtered.  For  the  re- 
mainder of  the  operation  this  method  is  the  same  as  the  first  method. 
The  fusing  of  the  residue  may  be  omitted  in  routine  work  in  a  given 
coal  if  it  is  certain  that  it  does  not  contain  phosphorous. 

Determination  of  volatile  matter  by  standard  method.  —  Apparatus: 
(i)    Platinum  crucible  with  tightly  fitting  cover  and  a  capacity  of 

not  less  than  10  c.c.  nor  more 
than  20  c.c.  Dimensions  to  be 
not  less  than  25  nor  more  than 
35  mm.  in  diameter  and  not 
less  than  30  nor  more  than  35 
mm.  in  height.  (2)  A  vertical 
electric  tube  furnace,  or  a  gas 
or  electrically  heated  muffle  fur- 
nace regulated  to  maintain  a 
temperature  of  950°  C.  (±  20° 
C.)  in  the  crucible  as  indicated 
by  a  thermometer  in  the  fur- 
nace (Fig.  8).  If  the  deter- 
mination of  volatile  matter  is 


not  an  essential  feature  of  the 
specifications  under  which  the 
coal  is  bought  a  Meker  burner 
may  be  used. 

Method:  In  a  weighed  plat- 
inum crucible  of  10  to  20  c.c. 
capacity,  closed  with  a  capsule 
cover,  i  gram  of  coal  is  placed. 
The  crucible  is  placed  on  platin- 
um or  nichrome-wire  supports  in  the  furnace  chamber  which  must  be 
kept  at  950°  C.  (±  20°  C.).  After  the  more  rapid  discharge  of 
volatile  matter  has  subsided,  as  indicated  by  the  dying  down  of  the 
flame,  the  cover  is  gently  tapped  to  close  the  crucible  more  tightly,  and 
thus  prevent  the  admission  of  air.  The  crucible  is  heated  just 
seven  minutes  and  then  removed  from  the  furnace  without  dis- 
turbing the  lid.  As  soon  as  cool  it  is  weighed.  The  loss  of  weight 
minus  moisture  equals  the  volatile  matter. 


inum 

\^     Platinnm- 

" Rhodium 

FIG.  8  —  Electric  furnace  for  deter- 
mination of  volatile  matter. 


DETERMINATION  OF  VOLATILE   MATTER  55 

For  subbituminous  coal,  lignite  or  peat,  a  modified  method  is 
employed  to  avoid  mechanical  loss  resulting  from  sudden  heating  of 
these  coals  high  in  volatile  matter.  This  consists  in  playing  a  burner 
flame  on  the  bottom  of  the  crucible  for  five  minutes  thus  gradually 
heating  it  to  a  high  temperature  before  it  is  placed  in  the  volatile- 
matter  furnace.  It  is  then  heated  in  the  furnace  for  six  minutes  at 
950°  C.  as  in  the  regular  method. 

Notes  and  precautions:  The  permissible  differences  in  duplicate 
determinations  are  as  follows: 


Same  analyst 

Different  analysts 

Bituminous  coals  

0.5  per  cent 

i  o  per  cent 

Lignites 

TO            " 

20         " 

The  cover  should  fit  close  enough  so  that  the  carbon  deposit  from 
bituminous  coal  or  lignite  does  not  burn  away  from  the  under. side  of 
the  lid.  Temperatures  should  be  carefully  regulated  to  the  stand- 
ards outlined. 

Other  methods:  According  to  the  preliminary  report  of  the  Joint 
Committee1  the  method  recommended  was  that  in  which  the  crucible 
of  10  c.c.  capacity  was  heated  for  seven  minutes  over  a  Bunsen  burner 
with  the  crucible  8  cm.  above  the  mouth  of  the  burner.  The  gas 
pressure  required  was  50  mm.  and  the  flame  about  18  cm.  in  height. 
The  burner  was  to  be  surrounded  with  a  refractory  cylinder  to  pre- 
vent air  currents  from  disturbing  the  flame.  The  specifications  for 
the  size  of  the  crucible  were:  2.4  cm.,  diameter  at  the  base,  3.4  cm. 
diameter  at  the  top  and  4  cm.  high.  This  method  is  still  used  where 
a  suitable  volatile-matter  furnace  is  not  available  although  a  Meker 
burner  is  more  reliable.  When  this  type  of  burner  is  used  the  crucible 
is  placed  2  cm.  above  the  orifice  with  a  flame  16  to  18  cm.  high.  A 
No.  3  Meker  is  the  type  specified.  These  methods  are  not  so  reliable 
as  that  with  a  proper  furnace  because  of  the  varying  conditions  which 
it  is  possible  to  have. 

Carnofs  method:  Carnot,  a  French  chemist,2  suggests  using  5 
grams  of  coal  in  a  platinum  or  porcelain  crucible,  the  size  of  which 

1  Jour.  Ind.  and  Eng.  Chem.  Vol.  5,  p.  517,  1913. 

2  Carnot,  Adolphe,  Traite  d'analyse  des  substances  minerales,  Vol.  I  and  II,  p.  205, 
1904. 


56  CHEMICAL  ANALYSIS  OF  COAL 

will  depend  upon  the  extent  to  which  the  coal  is  likely  to  swell.  The 
use  of  platinum  should,  however,  be  avoided  if  the  coal  contains 
pyrite,  and  most  coals  carry  some  of  this  mineral  although  not  always 
in  a  megascopic  condition.  The  crucible  is  covered  with  a  closely 
fitting  lid  and  placed  in  a  crucible  of  pottery  with  blocks  of  wood 
charcoal  surrounding  it.  The  charcoal  prevents  the  entrance  of 
oxygen  on  cooling.  The  clay  crucible  is  covered  with  a  lid,  placed  in 
a  calcination  furnace,  and  heated  for  half  an  hour  at  a  bright  heat. 
It  is  cooled,  the  small  crucible  wiped  clean  and  weighed.  Carnot 
has  also  used  a  muffle  furnace  and,  while  he  considers  the  Bunsen 
burner  method  the  simpler,  he  thinks  that  the  results  are  more  liable 
to  variation  than  those  obtained  by  using  a  furnace. 

Determination  of  fixed  carbon  by  standard  method.  —  Fixed  car- 
bon is  always  determined  by  difference  as  follows:  100  —  (per- 
centage moisture  +  percentage  ash  +  percentage  volatile  matter) 
=  fixed  carbon. 

Determination  of  sulphur  by  the  Eschka  method.1  —  While  such 
a  method  as  the  calorimeter  method  may  be  used  for  purposes  of 
control  in  such  a  laboratory  as  the  fuel-inspection  laboratory  of  the 
United  States  Bureau  of  Mines  no  other  method  is  considered  quite 
so  reliable  as  the  Eschka  method  although  it  is  not  so  rapid  as  some 
of  the  others. 

Apparatus:  (i)  Gas  or  electric  muffle  furnace,  or  burners  for 
igniting  the  coal  with  the  Eschka  mixture  arid  for  igniting  the  barium 
sulphate.  (2)  Porcelain,  silica  or  platinum  crucibles  or  capsules  for 
igniting  coal  with  the  Eschka  mixture.  (3)  No.  i  Royal  Meissen 
porcelain  capsule  i  inch  deep  and  2  inches  in  diameter.  This  capsule 
presents  more  surface  for  oxidation  and  it  is  more  convenient  to 
handle  than  the  ordinary  crucible.  (4)  No.  i  Royal  Berlin  porcelain 
crucibles  of  shallow  form  and  a  platinum  crucible  of  similar  size 
may  be  used.  (5)  No.  o  or  oo  porcelain  crucibles  or  platinum,  alun- 
dum  or  silica  crucibles  of  similar  size  must  be  used  for  igniting  the 
barium  sulphate. 

Solutions  and  reagents:     (i)  Barium  chloride.  —  Dissolve  100  grams 

of  barium  chloride  in  1000  c.c.  of  distilled  water      (2)   Saturated 

bromine  water.  —  Add  an  excess  of  bromine  to  1000  c.c.  of  distilled 

water.     (3)  Eschka  mixture.  —  Thoroughly  mix  2  parts;  by  weight, 

1  Oesterreichische  Zeitschr.    XXII,  p.  in,  1874. 


DETERMINATION  OF  SULPHUR  tf 

of  light  calcined  magnesium  oxide  and  i  part  of  anhydrous  sodium 
carbonate.  Both  materials  should  be  as  nearly  as  possible  free  from 
sulphur.  (4)  Methyl  orange;  —  Dissolve  0.02  gram  in  100  c.c.  of 
hot  distilled  water  and  then  filter.  (5)  Hydrochloric  acid.  —  Mix 
500  c.c.  of  hydrochloric  acid  (Sp.  gr.  1.20)  and  500  c.c.  of  distilled 
water.  (6)  Normal  hydrochloric  acid  —  Dilute  80  c.c.  of  hydro- 
chloric acid  (Sp.  gr.  1.20)  to  i  liter  with  distilled  water.  (7)  Sodium 
carbonate.  —  A  saturated  solution  taking  approximately  60  grams  of 
crystallized  or  22  grams  of  anhydrous  sodium  carbonate  in  100  c.c. 
of  distilled  water.  (8)  Sodium  hydroxide  solution.  —  Dissolve  100 
grams  of  sodium  hydroxide  in  i  liter  of  distilled  water.  This  solution 
may  be  used  in  place  of  the  sodium-carbonate  solution. 

Standard  Method:  Thoroughly  mix  on  glazed  paper  i  gram  of  coal 
and  3  grams  of  Eschka  mixture.  Transfer  the  mixture  to  a  No.  i 
Royal  Meissen  capsule,  a  No.  i  Royal  Berlin  crucible,  or  a  platinum 
crucible  of  similar  size.  Cover  with  about  i  gram  of  Eschka  mixture. 
Ignition  shall  be  performed  by  heating  the  crucible  over  an  alcohol, 
gasoline,  or  a  natural  gas  flame  or  in  a  gas  or  electrically  heated  muffle. 
Artificial  gas  must  not  be  used  owing  to  its  sulphur  content,  unless 
the  crucible  is  heated  in  a  muffle.  When  heated  over  a  flame  the 
crucible  is  placed  in  a  slanting  position  on  a  triangle  over  a  very 
low  flame.  This  is  necessary  to  avoid  rapid  expulsion  of  volatile 
matter  which  tends  to  prevent  complete  absorption  of  the  products 
of  combustion  of  the  sulphur.  The  crucible  is  heated  slowly  for 
thirty  minutes,  the  temperature  being  increased  gradually  and  the 
mixture  being  stirred  after  all  black  particles  have  disappeared.  The 
latter  condition  indicates  the  completeness  of  the  operation. 

If  the  crucible  is  heated  in  a  muffle,  it  should  be  placed  in  a  cold 
muffle  and  the  temperature  gradually  raised  to  87o°-975°  C.  (cherry- 
red  heat)  in  about  one  hour.  This  maximum  temperature  is  main- 
tained for  about  ij  hours  and  the  crucible  is  then  allowed  to  cool  in 
the  muffle. 

After  cooling,  the  contents  are  emptied  into  a  200  c.c.  beaker  and 
digested  with  100  c.c.  of  hot  water  for  one-half  to  three-quarters  of  an 
hour  with  occasional  stirring.  The  solution  is  filtered  and  the  residue 
washed  by  decantation.  After  several  washings  insoluble  matter  is 
transferred  to  the  filter  and  washed  five  times,  the  mixture  being 
kept  well  agitated.  The  filtrate  amounting  to  about  250  c.c.  is 


58  CHEMICAL  ANALYSIS  OF  COAL 

treated  with  10  to  20  c.c.  of  saturated  bromine  water  which  is  then 
made  slightly  acid  with  hydrochloric  acid  and  boiled  to  expel  the 
liberated  bromine.  The  so  ution  is  then  made  just  neutral  to  methyl 
orange  either  with  sodium  hydroxide  or  sodium  carbonate  solution 
and  i  c.c.  of  normal  hydrochloric  acid  is  then  added.  It  is  boiled 
again  and  10  c.c.  of  a  10  per  cent-solution  of  barium  chloride  (BaCl2- 
2H2O)  is  added  slowly  from  a  pipette  with  constant  stirring.  The 
boiling  is  continued  for  fifteen  minutes  and  the  solution  allowed  to 
stand  for  at  least  two  hours,  or  better  over  night,  at  a  temperature 
just  below  boiling.  It  is  filtered  through  an  ashless  filter  paper  and 
washed  with  hot  distilled  water  until  a  silver  nitrate  solution  shows 
no  precipitate  with  a  drop  of  the  filtrate.  The  wet  filter  containing 
the  precipitate  of  barium  sulphate  is  placed  in  a  weighed  platinum, 
porcelain,  silica  or  alundum  crucible,  free  access  of  air  being  allowed 
by  folding  the  paper  over  the  precipitate  loosely  so  as  to  prevent 
spattering.  The  paper  is  smoked  off  gradually  and  at  no  time  al- 
lowed to  burn  with  flame.  After  the  paper  is  practically  consumed  the 
temperature  is  raised  to  approximately  925°  C.  and  heated  to  constant 
weight. 

The  residue  of  magnesia,  etc.,  after  leaching  should  be  dissolved 
in  hydrochloric  acid  and  very  carefully  tested  for  sulphur.  If  an 
appreciable  amount  is  found  it  should  be  determined  quantitatively 
as  the  amount  of  sulphur  obtained  is  important. 

Blanks  and  Corrections:  A  correction  must  always  be  applied 
either  (i)  by  running  a  blank  exactly  as  described  above  using  the 
same  amount  of  all  reagents  that  were  employed  in  the  regular  de- 
termination, or  more  surely  (2)  by  determining  a  known  amount  of 
sulphate  added  to  a  solution  of  the  reagents  after  these  have  been  put 
through  the  prescribed  series  of  operations.  If  the  latter  procedure 
is  adopted  and  carried  out  once  a  week  or  whenever  a  new  supply  of 
a  reagent  must  be  used  and  for  a  series  of  solutions  covering  the 
range  of  sulphur  content  likely  to  be  met  with  in  coals,  it  is  only 
necessary  to  add  to  or  subtract  from  the  weight  of  barium  sulphate 
obtained  from  a  coal,  whatever  deficiency  or  excess  may  have  been 
found  in  the  appropriate  " check"  in  order  to  obtain  a  result  that  is 
more  certain  to  be  correct  than  if  a  " blank"  correction  as  determined 
by  the  former  procedure  is  applied.  This  is  due  to  the  fact  that  the 
solubility  error  for  BaSO4  for  the  amounts  of  sulphur  in  question  and 


SULPHUR  DETERMINED   BY  THE   BOMB   CALORIMETER  59 

the  conditions  of  precipitation  prescribed,  is  probably  the  largest 
one  to  be  considered.  BaSO4  is  soluble  in  acids  and  even  in  pure 
water  and  the  solubility  limit  is  reached  almost  immediately  on 
contact  with  the  solvent.  Hence,  in  the  event  of  using  reagents 
of  very  superior  quality  or  of  exercising  more  than  ordinary  precautions 
there  may  be  no  apparent  " blank"  because  the  solubility  limit  of 
the  solution  for  BaSO4  has  not  been  reached  or,  at  any  rate,  not 
exceeded. 

The  Atkinson  and  sodium-peroxide  methods  give  results  similar 
to  those  obtained  by  the  Eschka  method.  According  to  Register  if 
5  per  cent  of  nitrogen  is  present  in  the  gases  contained  in  the  bomb 
calorimeter,  the  sulphur  of  a  coal  is  almost  completely  oxidized  to 
H2SO4  and  the  washings  of  the  calorimeter  may  be  used  for  the  de- 
termination of  sulphur. 

The  permissible  differences  in  duplicate  determinations  are  as 
follows : 


Same  analyst 

Different  analysts 

Sulphur  under 

2  per  cent  

o  5  per  cent 

o  10  per  cent 

Sulphur  over  2 

per  cent  

O.IO            " 

o  .  20        " 

Sulphur  determined  by  the  bomb  calorimeter.  —  To  determine  the 
sulphur  content  of  a  coal  by  means  of  the  bomb  calorimeter  the 
washings  from  the  calorimeter  are  collected  in  a  250  c.c.  beaker. 
The  solution  is  titrated  with  standard  ammonia  (0.00587  gram  per 
c.c.)  to  make  the  "acid  correction"  for  the  heating  value,  methyl 
orange  being  used  as  an  indicator.  To  this  solution  is  added  5  c.c. 
of  dilute  hydrochloric  acid  (1:2)  and  it  is  then  raised  to  the  boiling 
point  before  filtering  off  any  insoluble  matter.  After  thorough  wash- 
ing, the  filtrate  is  boiled  and  the  sulphur  precipitated  with  barium 
chloride  as  in  the  Eschka  method.  The  percentage  of  sulphur  is 
then  derived  as  follows: 

Weight  of  BaS04  X  13. 74 

— ' — TTT  •  14. — £ —    — i —    *  =  percentage  of  sulphur. 
Weight  of  sample 

The  results  obtained  by  the  calorimeter  are  usually  3  to  8  per 
cent  lower  than  those  by  the  Eschka  method.  (For  a  further  note 
on  this  method  see  discussion  under  "The  bomb  calorimeter. " 


6o 


CHEMICAL  ANALYSIS  OF   COAL 


The  calorimetric  method  is  recommended  by  Parr1  who  also  uses 
it  for  sulphur  in  coke.  The  coke  is  pulverized  and  burned  in  the 
Parr  peroxide  calorimeter  with  sodium  peroxide  and  the  sulphur 
determined  in  the  washings. 

The  Photometric  Method  with  Turbidimeter.  —  There  are  many 
variations  of  the  photometric  method  but  they  can  only  be  used  for 
rough  determinations.  One  apparatus  which  seems  to  give  satis- 
factory results  is  a  modified  form  of  the  Jackson  candle  turbidimeter 
(Fig.  9).  This  is  one  type  of  the  turbidimeter  which  is  being  adop- 
ted by  many  analysts  for  rapid  determinations  of  sulphur  in  control 
work.  The  principle  of  this  apparatus  is  a 
brass  stand,  in  the  center  of  the  base  of  which 
there  is  a  holder  for  an  English  standard 
candle.  This  candle  is  regulated  so  that  a 
flame  30  to  40  mm.  long  is  maintained. 
Above  this  candle  is  a  horizontal  support  with 
a  hole  in  the  center.  Over  this  hole  a  grad- 
uated glass  cylinder  with  flat  polished  bottom 
is  placed  in  a  vertical,  opaque  cylinder  more 
than  half  the  height  of  the  glass  vessel. 
Since  this  apparatus  is  used  mainly  for  rapid 
water  analysis2  the  vessel  is  graduated  so 
that  the  lines  correspond  to  turbidities  pro- 
duced in  distilled  water  by  silica  when  present 
in  certain  parts  per  million.  A  25-centimeter  tube  may  show  tur- 
bidities of  100  to  5000  parts  per  million  of  silica  and  a  75-centimeter 
tube  25  to  5000  parts  per  million. 

The  early  designs  of  this  instrument  were  not  very  satisfactory  for 
the  determination  of  sulphur,  but  after  an  extended  series  of  experi- 
ments Muer3  found  that  with  certain  revised  tables  quite  satisfactory 
results  could  be  obtained.  A  series  of  experiments  by  this  modified 
method  gave  results  which  compare  favorably  with  those  obtained 
by  the  gravimetric  method.  The  method  as  outlined  as  is  follows: 
The  washings  from  the  bomb  calorimeter  amounting  to  about  150  c.c. 

1  Parr,  S.  W.,  Composition  and  character  of  Illinois  Coals.     111.  State  Geol.  Survey, 
Bull.  3,  p.  55,  1906. 

2  U.  S.  Geol.  Survey,  Water  supply  and  irrigation  paper  No.  651,  1905. 

3  Muer,  H.  F.,  The  determination  of  sulphur  in  coal  by  means  of  Jackson's  candle 
turbidimeter.     Jour.  Ind.  and  Eng.  Chem.,  Vol.  3,  p.  553,  1911. 


FIG.  9.  —  Jackson's  candle 
turbidimeter. 


THE   PHOTOMETRIC  METHOD   WITH   TURBIDIMETER  6l 

are  filtered  and  then  titrated  with  N/io  sodium  carbonate,  using 
methyl  orange  as  indicator.  The  titrated  solution  is  then  made  up 
to  200  c.c.  The  acidity  of  the  solution  may  be  taken  as  an  index 
of  the  amount  of  solution  to  be  taken  for  the  sulphur  test.  For 
anthracite  the  proportion  taken  is  i  to  £  and  for  soft  coals  J  to  TV 
of  the  whole.  This  portion  of  the  solution  is  measured  in  the  turbidi- 
meter  tube  diluted  to  near  the  100  c.c.  mark  on  the  tube.  It  is  shaken, 
acidified  with  i  c.c.  of  i  :  i  hydrochloric  acid  and  made  up  to  the 
100  c.c.  mark.  It  is  mixed  thoroughly  by  shaking.  A  tablet  of 
barium  chloride,  weighing  i  gram  and  having  been  compressed  without 
the  use  of  a  binder  is  placed  in  the  solution.  The  barium  chloride 
in  this  particular  form  seems  to  give  the  most  finely  divided  precip- 
itate and  therefore  the  best  results.  After  the  tablet  is  placed  in 
the  tube  the  latter  is  closed  by  a  clean  rubber  stopper  and  then  rolled 
gently  until  the  precipitation  of  the  sulphur  is  complete.  The  turbid 
liquid  is  transferred  to  a  beaker.  The  candle  is  lighted,  the  gradu- 
ated tube  is  put  in  place,  and  enough  of  the  liquid  is  at  once  poured 
in  to  prevent  the  tube  from  cracking.  The  liquid  is  then  gradually 
poured  in,  being  allowed  to  run  down  the  side  of  the  tube,  until  the 
flame  becomes  dim  as  one  looks  down  the  tube.  The  liquid  is  then 
added  very  slowly  until  the  flame  just  disappears.  The  depth  of  the 
liquid  in  centimeters  is  noted,  the  liquid  returned  to  the  beaker  and 
a  new  reading  made.  This  process  is  repeated  until  a  good  average 
reading  is  obtained.  Knowing  the  depth  of  the  liquid  in  centi- 
meters the  weight  of  sulphur  and  sulphur  trioxide  in  milligrams  may 
be  obtained  from  a  table  which  Muer  has  prepared.  In  his  experi- 
ments he  found  that  for  a  depth  of  less  than  2.5  cm.  of  liquid  there 
was  a  sharp  deviation  from  a  straight  line  curve  in  which  the  increase 
in  depth  in  centimeters  was  inversely  proportional  to  the  weight  of 
sulphur  in  milligrams.  This  variation  seems  to  be  due  to  the  lens 
effect  of  the  bottom  of  the  tube  and  to  avoid  it  the  solution  should 
be  diluted  so  that  the  depth  will  be  greater  than  2.5  cm.  For  depths 
above  17.0  cm.  there  was  also  a  marked  variation  from  the  straight 
line  and  to  avoid  this  it  is  better  to  concentrate  the  solution.  For 
all  readings  between  these  two  limits  it  was  found  that  the  following 
formula  is  applicable: 


62  CHEMICAL   ANALYSIS   OF   COAL 

where  S  is  the  weight  of  sulphur  in  milligrams  and  C  is  the  depth  of 
the  liquid  in  centimeters  at  the  time  the  flame  becomes  obscured. 

Methods  for  determining  the  proportions  of  the  various  forms  of 
sulphur  in  coal.  —  In  a  recent  article  Powell  and  Parr1  have  enumer- 
ated methods  for  determining  the  proportions  of  the  various  forms 
of  sulphur  in  coal,  as  follows :  For  sulphate  sulphur  the  coal  is  treated 
with  hydrochloric  acid  after  fine  grinding.  A  sample  of  5  grams  is 
treated  with  300  c.c.  of  a  3-per  cent  solution  of  the  acid,  for  forty 
hours  at  60°  C.  The  solution  is  filtered  and  the  filtrate  analyzed  for 
sulphur  as  in  the  regular  method  by  precipitation  with  barium  chlo- 
ride (BaCl2).  For  the  pyrite  sulphur  determination  the  sulphate 
sulphur  is  first  removed  as  described  above  with  hydrochloric  acid 
and  the  coal  is  then  treated  with  nitric  acid.  A  i-gram  sample  of  the 
finely  powdered  coal  is  employed  and  about  80  c.c.  of  nitric  acid 
(i  part  HNOs  sp.  gr.  1.42  to  3  parts  water,  resulting  sp.  gr.  about 
1.12)  is  used.  The  solution  stands  at  room  temperature  for  twenty- 
four  hours  before  being  filtered.  The  nitric  acid  is  disposed  of  by 
evaporating  the  filtrate  to  dryness  and  after  taking  up  with  a  little 
hydrochloric  acid  the  sulphur  is  precipitated  by  barium  chloride 
(BaCl2). 

The  resinic  sulphur  is  determined  by  treating  the  coal  with  phenol: 
this  treatment  involves  prolonged  extraction  with  this  reagent.  The 
other  form  of  organic  sulphur,  known  as  the  humus  sulphur,  is  de- 
termined directly  by  taking  the  residue  from  the  nitric  acid  extraction 
and  adding  25  c.c.  ammonium  hydroxide  (sp.  gr.  0.90).  This  mix- 
ture is  allowed  to  stand  for  several  hours;  it  is  then  diluted,  passed 
through  a  large  filter  and  the  filtrate  evaporated  to  dryness.  The 
sulphur  may  then  be  determined  in  the  usual  manner  by  fusing  the 
residue  with  sodium  peroxide.  It  is  evident  that  the  total  organic 
sulphur  may  be  determined  by  subtracting  the  sum  of  the  sulphate 
and  pyrite  sulphur  determinations  from  the  total  sulphur,  or  the 
humus  sulphur  might  be  determined  by  difference  between  total  sul- 
phur and  the  sum  of  the  other  three  types. 

Sulphur  in  ash.  —  A  determination  of  sulphur  in  the  ash  may  be 
made  by  placing  the  ash  in  an  evaporating  dish,  adding  hydrochloric 
acid,  evaporating  to  dryness,  then  taking  up  with  hydrochloric  acid 

1  Powell,  A.  R.,  and  Parr,  S.  W.,  Forms  in  which  sulphur  occurs  in  coal.  Trans. 
Amer.  Inst.  Min.  Met.  Eng.,  Vol.  LXIII.  p.  674,  1920. 


DETERMINATION  OF  CARBON  AND  HYDROGEN 


and  hot  water.  This  solution  is 
filtered  and,  after  washing,  the  sul- 
phur is  precipitated  as  barium  sul- 
phate (BaSO4)  by  adding  barium 
chloride  (BaCl2).  From  the  result 
obtained  the  combustible  sulphur  in 
the  coal  may  be  determined  by  sub- 
tracting the  above  result  from  the 
total  sulphur.1 

Ultimate  Analysis 

Determination  of  carbon  and  hy- 
drogen. —  The  determination  of  car- 
bon and  hydrogen  is  made  with  a 
combustion  furnace,  either  gas  or 
electric.  The  gas  furnace  used  is 
usually  the  Glaser  type  with  twenty- 
five  burners.  The  Fletcher  furnace 
is  often  used  in  England.  The  prin- 
ciple involved  is  the  complete  oxida- 
tion of  the  carbon  and  hydrogen  by 
passing  the  products  of  combustion 
over  red-hot  copper  oxide.  The  sul- 
phur is  taken  up  by  lead  chromate. 

Description  of  the  furnace:  The 
apparatus  consists  of  a  purifying 
train  in  duplicate,  a  combustion  tube 
and  an  absorption  train  (Fig.  10). 
The  purifying  train  is  in  duplicate 
so  that  oxygen  may  be  fed  from  a 
gas  vessel,  such  as  a  Linde  oxygen 
cylinder,  through  one  set  of  tubes 
and  air  through  the  other.  It  is 
connected  to  the  combustion  tube  by 
a  three-way  tap  so  that  the  currents 
may  be  regulated.  The  air  and  oxy- 
gen are  first  passed  through  sul- 

1  Pollard.     Op.  cit.,  p.  9. 


64  CHEMICAL  ANALYSIS  OF  COAL 

phuric  acid,  then  through  a  30  per  cent  potassium  hydroxide  solution, 
then  over  soda  lime  and  granular  calcium  chloride  in  a  U-tube. 
Some  English  analysts  use  two  U-tubes  filled  with  pumice  saturated 
with  sulphuric  acid,  the  pumice  having  previously  been  ignited  with 
sulphuric  acid  to  remove  chlorides  and  other  impurities,  in  place  of  the 
soda  lime  and  calcium  chloride  tube  A  small  bottle  of  sulphuric 
acid  may  be  connected  in  series  next  to  the  combustion  tube  for  the 
purpose  of  indicating  the  rate  at  which  the  gases  are  being  fed  to 
the  combustion  tube. 

The  combustion  tube  should  be  from  100  to  no  cm.  in  length  by 
about  21  mm.  in  external  or  12  to  15  mm.  internal  diameter.  It 
should  be  of  hard  Jena  or  similar  glass. 

The  absorption  train  consists  of  a  Marchand  tube  filled  with  gran- 
ular calcium  chloride  (CaCl2)  for  absorption  of  the  water.  Instead 
of  this  material  a  U-tube  filled  with  pumice  saturated  with  sulphuric 
acid  may  be  used.  If  the  acid  be  used  it  is  well  to  fill  the  tube,  allow 
it  to  stand  over  night  and  then  drain  off  the  acid  just  before  using. 
Following  the  Marchand  tube  there  is  a  Liebig  or  Geissler  bulb  filled 
with  30  per  cent  potash  solution  to  absorb  the  carbon  dioxide  given 
off.  This  solution  should  be  treated  with  a  little  potassium  perman- 
ganate for  the  purpose  of  oxidizing  any  ferrous  iron  or  nitrates.  In 
place  of  this  solution  powdered  potash  is  often  used.  A  guard  tube 
comes  next  and  is  filled  with  soda  lime  and  granular  calcium  chloride 
so  as  to  absorb  any  traces  of  carbon  dioxide  and  moisture  which  have 
passed  the  other  tubes.  Some  analysts  use  sulphuric  acid  and  pumice 
for  this  purpose. 

Testing  the  apparatus:  To  prepare  the  apparatus  for  a  determin- 
ation care  should  be  taken  to  see  that  all  the  reagents  used  are  fresh 
and  pure.  A  blank  test  may  be  run  by  passing  about  a  liter  of  air 
through  the  train,  heated  as  in  a  regular  test;  if  there  is  a  change  in 
weight  in  the  absorption  tubes  of  less  than  0.5  mg.  each  the  apparatus 
is  considered  ready  for  use. 

Method  of  making  the  determination  with  furnace:  The  sample  of 
dry  coal  ground  to  50  or  6o-mesh  is  weighed  into  a  platinum  or  por- 
celain boat.  The  weight  of  the  sample  used  varies  with  different 
analysts,  some  considering  that  a  o. 5-gram  sample  is  best  while  others 
use  a  o.2-gram  sample.  The  latter  is  recommended  by  the  analysts 
of  the  United  States  Bureau  of  Mines.  The  boat  containing  the 


DETERMINATION  OF.  CARBON  AND   HYDROGEN  65 

sample  is  kept  in  a  weighing  tube  to  exclude  moisture  while  prepar- 
ations are  being  made  for  placing  it  in  the  combustion  tube. 

The  combustion  tube  is  filled  in  different  ways  by  different  analysts. 
For  example,  Pollard  leaves  a  space  of  10  cm.  at  each  end  of  the  tube. 
The  space  is  followed  by  6-8  cm.  of  copper-oxide  roll;  16-20  cm. 
for  the  boat;  45  cm.  of  copper  oxide;  8  cm.  lead  chromate;  and 
10  cm.  of  silver  spiral.  Stan  ton  and  Fieldner  leave  the  first  30  cm. 
of  the  tube  empty.  This  space  is  followed  by  an  asbestos,  acid- 
washed  and  ignited  plug,  or  a  roll  of  copper  gauze.  Following 
this  is  40  cm.  filled  loosely  with  copper-oxide  wire.  The  wire  is 
separated  from  10  cm.  of  lead  chromate  by  another  asbestos  plug. 
A  third  asbestos  plug  20  cm.  from  the  end  of  the  tube  keeps  the 
chromate  in  place. 

The  combustion  tube  containing  the  boat  in  which  the  coal  is  spread 
out  flat  is  connected  in  the  train  and  the  train  is  connected  with  an 
aspirator  which  produces  a  steady  suction.  The  suction  may  be 
kept  constant  by  using  a  Mariotte  flask.  It  is  easier  to  keep  the 
joints  tight  if  the  gases  be  drawn  through  the  apparatus  than  if  they 
be  forced  through  by  pressure.  A  satisfactory  test  for  the  tightness 
of  the  apparatus  is  to  draw  air  through  the  potash  bulb  at  the  rate  of 
three  bubbles  per  second.  The  three-way  tap  is  then  closed  and  if 
not  more  than  three  bubbles  of  gas  pass  the  potash  bulb  per  minute 
it  is  considered  satisfactory. 

When  the  boat  is  placed  in  the  combustion  tube  care  must  be  taken 
to  have  the  copper  oxide  at  a  bright  red  heat  and  the  lead  chromate 
at  a  dull  red  before  the  coal  is  heated.  Otherwise  methane  may 
escape  combustion.  Before  the  coal  is  heated  a  current  of  oxygen 
is  passed.  The  coal  must  be  heated  gradually;  otherwise  too  much 
tarry  matter  may  be  driven  off  in  a  short  space  of  time  to  permit 
complete  combustion.  The  heat  is  increased  gradually  and  the  cur- 
rent of  oxygen  is  maintained  for  about  two  minutes  after  the  sample 
ceases  to  glow  when  it  is  turned  off  and  about  1200  c.c.  of  air  is  drawn 
through  the  train. 

The  absorption  bulbs  or  tubes  are  disconnected  and  weighed. 
The  hydrogen  percentage  in  a  o.  2-gram  sample  is  determined  by 
multiplying  the  increase  in  weight  in  the  calcium  chloride  tube  by 
55.55  and  the  carbon  percentage  by  multiplying  the  increase  in 
weight  in  the  potassium  hydroxide  bulb  by  136.36.  It  is  evident  that 


66  CHEMICAL  ANALYSIS  OF   COAL 

the  percentage  of  carbon  will  vary  slightly  if  there  are  carbonates  in 
the  coal  and  the  hydrogen  will  vary  if  there  are  hydrous  minerals  or 
moisture  present. 

The  ash  in  this  sample  may  be  weighed  and  its  percentage  also 
determined.  Duplicates  should  agree  within  o.i  per  cent  for  hy- 
drogen and  0.2  per  cent  for  carbon. 

A  convenient  electric  furnace  of  the  Heraeus  type  may  be  used 
in  place  of  the  gas  combustion  furnace.  This  furnace  as  used  by 
Stanton  and  Fieldner1  consists  of  three  independent  heaters.  Two 
of  these  are  on  wheels  and  mounted  on  a  track  so  that  they  are  mov- 
able. The  third  one  is  stationary  around  the  tube  where  the  lead 
chromate  is  located.  The  stationary  heater  is  not  a  part  of  the 
regular  Heraeus  furnace  but  it  was  added  by  winding  an  alundum 
tube  12  cm.  long  with  No.  16  nichrome  II  wire  and  enclosing  it  in  a 
cylinder  packed  with  magnesia-asbestos. 

The  movable  heaters  have  very  thin  platinum  foil,  weighing  about 
9  grams  in  all,  wound  on  a  porcelain  tube  of  30  mm.  internal  diameter. 
The  combustion  tube  is  about  21  mm.  external  diameter  and  900 
mm.  in  length.  It  consists  of  Jena  glass  or  fused  silica.  It  is  sup- 
ported in  an  asbestos-lined  nickel  trough.  Each  heater  has  a  separate 
rheostat  and  the  current  required  is  about  4.5  amperes  with  220 
volts. 

The  purifying  train  consists  of  a  Tauber  s  drying  apparatus  which 
contains  sulphuric  acid,  a  30  per  cent  potassium  hydroxide  solution 
of  granular  soda  lime  and  calcium  chloride.  The  absorption  train 
consists  of  a  5 -inch  U-tube  containing  granular  calcium  chloride; 
a  Vanier  potash  bulb  containing  a  30  per  cent  potassium  hydroxide 
solution  and  granular  calcium  chloride;  a  guard  tube,  containing 
granular  calcium  chloride  and  soda  lime;  and  a  Mario tte  flask  for 
preserving  a  constant  pressure.  The  calcium  chloride  used  in  the 
tube  should  be  saturated  with  carbon  dioxide  before  using  by  being 
placed  in  a  large  drying  jar  and  having  the  jar  filled  with  carbon 
dioxide.  The  jar  is  left  over  night  and  dry  air  is  then  drawn  through 
it  to  remove  the  carbon  dioxide.  The  saturated  material  may  then 
be  kept  in  tightly  stoppered  bottles. 

It  is  possible  with  this  furnace  to  so  adjust  the  heaters  that  the 
tube  may  be  dried  carefully,  the  lead  chromate  may  be  kept  hot  and 

1  Op.  cit.,  p.  22. 


DETERMINATION  OF  CARBON  AND   HYDROGEN 


67 


the  copper  oxide  may  be  raised  to  a  red  heat  before  the  boat  con- 
taining the  sample  is  heated  to  a  high  temperature.  The  boat  is 
then  heated  until  all  the  carbon  is  burned  off  as  indicated  by  the  fact 
that  the  residue  ceases  to  glow.  The  tubes  are  then  weighed  and  the 
calculation  made  as  in  the  determination  described  above  with  the 
gas  combustion  furnace. 

In  addition  to  the  methods  described  above  Parr1  has  described  a 
process  for  determining  total  carbon  with  the  improved  Parr  Calor- 
imeter. 

A  description  of  this  calorimeter  is  as  follows:  A  A  (Fig.  na),  is 
a  liter  can  for  water;  BB  and  CC  are  insulating  vessels  of  indurated 
fiber;  D  is  a  cartridge  to  receive  the  charge  of  coal  and  chemicals. 


Fig.  ii. —  (a)  Parr  peroxide  bomb  calorimeter.     (V)  Bomb  enlarged. 

It  rests  on  the  pivot  F  and  is  made  to  revolve  by  means  of  the  pulley  P. 
The  small  turbine  wings  produce  complete  circulation  of  the  water. 
The  temperature  is  recorded  on  the  thermometer  T.  Figure  nb  is 
an  enlargement  of  the  bomb  or  cartridge  which  has  been  improved 
by  placing  the  air  chambers  around  the  inner  shell.  These  chambers 
contain  air  which  the  sudden  rise  in  temperature  expels.  The  air 

1  Op.  cit. 


68  CHEMICAL  ANALYSIS  OF  COAL 

at  first  prevents  the  cooling  of  the  sides  of  the  chamber  to  such  a 
point  that  the  chemical  action  around  the  walls  is  checked  and  then 
on  being  expelled  it  permits  the  cooler  water  to  come  into  contact 
with  the  hot  walls  of  the  shell  and  produce  a  more  rapid  transfer 
of  heat  and  consequently  greater  efficiency. 

Parr  used  sodium  peroxide  and  the  reaction  is  approximately  as 
follows: 


56  Na2O2  +  C25Hi8O3  =  25  Na2CO3  +  iSNaOH  +  22Na2O. 

Sodium  Coal  Sodium  Sodium  Sodium 

peroxide  carbonate  hydrate  oxide 

For  such  substances  as  coke,  petroleum,  and  anthracite  a  more 
vigorous  oxidizing  medium  is  used.  The  most  effective  is  a  mixture 
of  potassium  chlorate  and  nitrate  in  proportion  of  i  to  4  and  used 
with  sodium  peroxide  in  proportion  of  i  to  10.  This  was  used  to 
good  advantage  on  the  slaty  coals. 

Parr  devised  this  method  in  order  that  there  might  be  some  ready 
means  of  obtaining  the  total  carbon  as  this  was  necessary  in  his 
classification  of  coals.  He  also  devised  a  curve  from  which  can  be 
read  the  percentage  of  combustible  or  available  hydrogen  when  the 
carbon  content  is  known.  The  curve  is  based  on  the  principle  that 
there  is  a  more  or  less  definite  relation  in  the  various  coals  between 
the  total  carbon,  the  fixed  carbon,  and  the  "  available"  hydrogen. 
(For  a  discussion  of  the  subject  of  available  hydrogen  in  coal,  see 
Parr's  Classification  in  Chapter  5.) 

The  determination  of  nitrogen.  —  The  method  usually  employed 
for  the  determination  of  nitrogen  is  the  modified  Kjeldahl-  Gunning 
method.1  A  gram  of  coal  is  placed  in  a  500  c.c.  Kjeldahl  flask  to- 
gether with  30  c.c.  of  concentrated  sulphuric  acid,  5  to  8  grams  of 
potassium  sulphate  (K2SO4)  and  0.6  grams  of  mercury.  Mercury 
oxide  may  be  used  instead  of  mercury,  but  a  gram  of  the  oxide  is 
necessary.  The  solution  should  be  boiled  until  the  coal  is  all  oxi- 

1  Dyer,  B.,  Kjeldahl's  method  for  the  determination  of  nitrogen.  Jour.  Chem.  Soc., 
Vol.  67,  pp.  811-817,  l895-  Also,  Trescot,  T.  C.,  Comparison  of  the  Kjeldahl-Gunning- 
Arnold  method  with  the  official  Kjeldahl  and  official  Gunning  method  of  determining 
nitrogen.  Jour.  Ind.  Eng.  Chem.,  Vol.  5,  pp.  914-915,  1913  and  Wedemeyer,  K.,  Ein 
Wort  zur  Stickstoffbestimmung  nach  Kjeldahl-Gunning.  Chem.  Ztg.  Jahrg.  22.  p.  21, 
1898. 


THE   DETERMINATION  OF   NITROGEN  69 

dized  and  the  solution  has  become  practically  colorless.  The  boiling 
may  require  two  hours  or  more,  depending  upon  the  nature  of  the 
coal.  The  solution  is  allowed  to  cool  and  a  little  potassium  perman- 
ganate (K  Mn  O4)  is  added  or  it  may  be  added  without  cooling. 
Some  analysts  add  this  while  the  solution  is  hot,  while  others  cool 
it  first.  After  boiling  for  an  hour,  the  permanganate  is  added  to- 
gether with  more  mercury  and  then  boiled  again  until  complete 
oxidation  results. 

The  solution  is  cooled  and  diluted  to  about  200  c.c.  with  cold  water. 
To  this  is  added  20  to  25  c.c.  of  potassium  sulphide  (K2S)  solution 
(40  grams  per  liter)  to  precipitate  the  mercury.  Sodium  sulphide 
(Na2S)  of  same  strength  is  sometimes  used  in  place  of  the  potassium 
sulphide.  A  little  zinc  is  added  to  prevent  bumping  and  then  about 
80  to  100  c.c.,  or  enough  to  make  the  solution  alkaline,  of  a  50  per 
cent  solution  of  sodium  hydroxide  (NaOH).  The  Kjeldahl  flask  is 
at  once  connected  with  the  condenser  and  the  ammonia  is  distilled 
over  into  a  measured  amount  (usually  10  c.c.)  of  standard  sulphuric 
acid,  to  which  cochineal  indicator  is  added  for  titration.  The  dis- 
tillation is  continued  until  about  200  c.c.  has  passed  over.  The 
distillate  is  then  titrated  with  standard  ammonia  solution.  (In  this 
case  20  c.c.  NH4OH  =  10  c.c.  H2SO4  =  0.05  grams  nitrogen.) 

Pollard1  states  that  the  following  modification  was  used  in  the 
English  Government  laboratory  with  good  results,  a  sharper  end- 
point  being  obtained  by  this  method  than  in  the  former  practice. 
The  duplicates  agreed  to  within  0.05  per  cent.  To  i  gram  of  coal 
30  c.c.  of  pure,  concentrated  sulphuric  acid  containing  i  gram  of 
salicylic  acid  was  added.  The  vessel  was  kept  cool  by  being  im- 
mersed in  water  while  the  acid  was  added.  To  this  solution  5  grams 
of  sodium  thiosulphate  were  carefully  added  and  then  7  grams  of 
potassium  sulphate,  followed  by  a  crystal  of  copper  sulphate.  This 
mixture  was  heated  gradually  at  first  and  then  strongly  until  complete 
oxidation  occurred.  It  was  cooled,  and  distilled  with  excess  of  soda 
and  a  little  sodium  sulphide  in  the  usual  way,  into  25  c.c.  of  N/io 
sulphuric  acid.  The  excess  of  soda  was  determined  by  adding  to  the 
solution  10  c.c.  of  a  10  per  cent  solution  of  potassium  iodide,  the 
liberated  iodine  being  determined  in  the  usual  way.  Pollard's  use 
of  copper  sulphate  is  interesting  in  view  of  the  fact  that  Fieldner  and 

1  Op.  cit.,  p.  9. 


70  CHEMICAL   ANALYSIS  OF  COAL 

Taylor1  found  that  copper  sulphate  was  not  as  good  a  catalytic  agent 
as  mercury. 

The  determination  of  oxygen.  —  A  great  many  different  analytical 
methods  have  been  suggested  for  the  determination  of  oxygen  but 
none  of  them  are  sufficiently  simple  or  accurate  to  be  generally  ac- 
cepted.2 The  scheme  almost  universally  adopted  is  to  obtain  oxy- 
gen by  difference,  the  sum  of  carbon,  hydrogen,  nitrogen,  sulphur,  and 
ash  being  subtracted  from  100  per  cent.  This  has  one  great  disad- 
vantage because  it  throws  upon  the  oxygen  the  accumulated  errors 
in  the  determination  of  carbon,  hydrogen,  nitrogen,  sulphur  and  ash. 
These  errors  may  tend  to  balance  one  another  to  some  extent  but 
there  are  many  indefinite  factors  which  may  affect  the  result.  If  the 
coal  contains  iron  pyrite  this  tends  to  make  the  oxygen  too  low;  if 
it  contains  argillaceous  materials,  which  would  naturally  carry  water 
of  composition,  the  oxygen  in  the  coal  will  be  too  high.3  Carbonates 
from  the  coal,  as  already  pointed  out,  will  have  a  bearing  on  the 
proportions  of  oxygen  and  carbon  in  the  coal.  This  is  because  there 
is  no  means,  with  our  present  methods,  of  distinguishing  between 
the  carbon  and  oxygen  from  the  coal  and  that  from  the  carbonates 
unless  an  analysis  of  the  ash  be  made  and  the  various  constituents 
computed  in  terms  of  carbonates,  sulphides,  etc.,  an  operation  which 
cannot  be  carried  out  in  practice. 

Some  of  the  methods  used  for  the  direct  determination  of  oxygen 
in  coal  are  based  on  the  following  principles:  Baumhauer4  en- 
deavored to  reoxidize  the  copper  reduced  in  the  combustion  tube. 
He  also  employed  iodate  of  silver.  Mitscherlich5  has  used  at  different 
times  a  current  of  chlorine  which  united  with  hydrogen  to  form 
hydrochloric  acid,  leaving  the  oxygen  free  or  to  unite  with  carbon, 
and  mercury  dioxide.  Since  a  certain  amount  of  oxygen  must  be 
supplied  in  addition  to  that  in  the  coal  in  order  to  produce  complete 

1  Fieldner,  A.  C.,  and  Taylor,  C.  A.,  Determination  of  nitrogen  in  coal.     U.  S.  Bur. 
of  Mines,  Tech.  Paper  64,  p.  22,  1915. 

2  For  a  good  summary  of  various  methods  see  Carnot,  Op.  cit.,  p.  229. 

3  Parr,  S.  W.,  An  initial  coal  substance  having  a  constant  heating  value.     111.  State 
Geol.  Survey;  Bull.  8,  1907. 

4  Baumhauer,   E.H.V.,  Ueber  die  Elementaranalyse  organische   Korper.     Zeitschr. 
f.  Analyt.  Chem.,  Vol.  V,  p.  143,  1866. 

8  Mitscherlich,  A.,  Neue  Methoden  zur  Bestimmung  der  Zusammensetzung  organischer 
Verbindungen,  Zeitschr.  f.  Analyt.  Chem.,  Vol.  VI,  p.  136,  1867. 


DETERMINATION  OF  THE   CALORIFIC   VALUE  71 

combustion  it  is  supplied  by  the  mercury  dioxide  and  its  weight  can 
be  determined. 

Maumene1  has  employed  litharge  and  calcium  phosphate  and  has 
calculated  the  oxygen  supplied  by  the  litharge  for  combustion  of 
the  organic  material. 

Determination  of  the  Calorific  Value 

The  calorific  value  of  a  coal  is  the  heat  developed  by  the  com- 
bustion of  a  unit  weight  of  the  substance.  It  is  usually  expressed  in 
terms  of  the  calorie  or  the  British  thermal  unit  (B.t.u.).  The  cal- 
orie is  the  unit  in  the  metric  system  and  the  standard  calorie  is  the 
heat  required  to  raise  i  gram  of  water  i°  C.  at  the  point  of  its  greatest 
density  (4°  C.).  It  is,  however,  often  stated  more  conveniently  as 
the  heat  required  to  raise  one  gram  of  water  from  15°  to  16°  C.  The 
large  calorie  is.  the  same  except  that  a  kilogram  of  water  is  used  in- 
stead of  a  gram. 

The  standard  British  thermal  unit  (B.t.u.)  which  is  generally 
employed  by  English-speaking  engineers  is  the  heat  required  to  raise 
i  pound  of  water  from  39.1°  F.  to  40.1°  F.,  this  corresponding  in  the 
English  system  to  the  point  of  greatest  density  of  the  water.  In 
recent  years  the  unit  is  often  described  as  the  heat  required  to  raise 
i  pound  of  water  from  60°  to  61°  F.,  or  from  62°  to  63°  F.,  as  this  is  a 
little  more  convenient  and  the  latter  figures  are  usually  adopted  in 
practice.  The  difference  in  all  these  cases  is  very  small. 

To  express  calories  as  British  thermal  units,  multiply  the  number 
of  calories  by  f  or  1.8. 

The  calorific  value  is  sometimes  expressed  as  the  real  calorific  value 
and  sometimes  as  the  industrial  calorific  value.  The  real  calorific 
value  is  the  result  obtained  when  complete  combustion  occurs  in  the 
laboratory  in  an  apparatus  such  as  the  calorimeter  and  the  industrial 
calorific  value  is  the  value  obtained  when  the  coal  is  burned  under  a 
boiler.  The  latter  result  approaches  much  more  closely  that  which 
is  obtained  in  industrial  operations  and  it  is  always  lower,  owing  to 
various  losses,  than  the  real  value.  It  is  measured  as  the  heat  neces- 
sary to  vaporize  large  quantities  of  water  and  the  weight  of  the  coal 
used  in  some  cases  may  be  1500  to  2000  kilograms. 

1  Maumene,  J.,  Compt.  Rend.,  Vol.  55,  p.  432,  1862. 


72  CHEMICAL  ANALYSIS  OF  COAL 

The  Bomb  Calorimeter 

The  calorimeter  in  some  form  has  been  in  use  at  least  since  the 
time  of  Laplace  and  Lavoisier  and  it  was  practically  perfected  by 
Berthelot  and  Vielle,  but  it  was  not  until  Mahler  took  up  the  work 
for  the  Societe  d'Encouragement  a  ITndustrie  Nationale  in  France 
that  a  satisfactory  calorimeter  for  practical  uses  was  designed.  The 
early  calorimeters  contained  a  great  deal  of  platinum  and  this  made 


Fig.  12. —  Emerson  fuel  calorimeter  with  diagram  of  bomb  and  pressure 
gauge  and  details  of  the  ignition  wiring. 

them  very  expensive.  The  Mahler  bomb  calorimeter  was  so  much 
cheaper  and  so  efficient  that  this  general  type,  now  known  under 
many  modifications,  is  almost  universally  adopted.  The  calori- 
meters which  may  be  used  for  standard  determinations  are  the  Em- 
erson, Atwater,  Davis,  Peters,  Parr,  Mahler  and  Williams  or  similar 
types.  One  of  the  requirements  is  an  inner  surface  of  platinum,  gold, 
porcelain,  enamel  or  other  material  which  is  not  attacked  by  products 
of  combustion  such  as  sulphuric  and  nitric  acids. 


DETERMINATION  BY  CALORIMETER  73 

Determination  by  calorimeter.  —  To  determine  the  calorific  value 
by  means  of  one  of  these  calorimeters  of  the  Mahler  type,1  place  i 
gram  of  6o-mesh  coal  on  an  asbestos  mat  in  the  platinum  tray.  The 
asbestos  should  be  washed  and  ignited  before  using.  The  terminals 
of  the  firing  circuit  are  connected  by  about  13  mg.  of  fine  iron  wire 
about  105  mm.  long  by  0.16  mm.  in  diameter.  Platinum  wire  should 
be  used  if  the  bomb  is  platinum-lined  and  care  must  be  taken  to  see 
that  the  terminals  are  clean.  The  wire  is  pressed  down  on  the  coal 
and  the  tray  placed  in  the  bomb.  The  lid  is  screwed  down  tightly 
on  the  lead  gasket.  Oxygen  is  forced  into  the  bomb  very  slowly 
until  the  pressure  within  the  bomb  reaches  1 8  to  20  atmospheres  with 
the  needle-point  valve  closed  just  tight  enough  to  avoid  leakage. 

The  brass  bucket  is  placed  in  the  insulating  jacket  and  the  bomb, 
full  of  oxygen,  is  placed  in  the  brass  bucket  which  contains  about 
2000  to  2500  c.c.  of  distilled  water.  The  quantity  of  water  used 
varies  with  the  type  of  calorimeter. 

The  stirring  apparatus  is  adjusted  so  that  it  does  not  strike  the 
bomb  or  bucket.  The  thermometer,  which  is  graduated  to  0.01°  C.  or, 
better,  to  0.001°  C.,  must  not  touch  any  metal  parts  and  its  bulb 
should  be  about  5  cm.  from  the  bottom  of  the  bucket.  The  terminals 
of  the  bomb  are  connected  with  wires  leading  to  the  switch.  After 
the  stirrer  has  been  in  motion  until  the  water  is  thoroughly  mixed  the 
first  reading  of  the  thermometer  is  taken  by  means  of  a  reading 
telescope  attached  to  a  ca  the  tome  ter.  The  stirring  is  continued 
uniformly  during  the  test  and  in  a  covered  calorimeter  trie  temperature 
should  never  be  allowed  to  rise  more  than  i°  C.  above  that  of  the 
water  jacket. 

Taking  readings:  The  time  required  for  the  determination  may 
be  divided  into  the  preliminary  period,  the  combustion  period  and  the 
final  period.  In  the  preliminary  period  five  readings  are  usually 
taken  one  minute  apart  until  the  rate  of  change  per  minute  is  prac- 
tically constant.  After  the  fifth  reading  is  taken  a  current  of  75 
volts  is  turned  on  for  about  one-half  second  thus  starting  the  com- 
bustion period.  The  first  two  readings  in  this  period  are  taken  one- 
half  minute  apart  because  of  the  great  change  in  ratio.  The  tem- 
perature rises  to  a  maximum  and  then  begins  to  fall.  The  readings 

1  Lord,  N.  W.,  and  others.  Analysis  of  coals.  U.  S.  Bur.  of  Mines,  Bull.  22,  Part  I, 
p.  17,  1913.  Also  Stanton  and  Fieldner,  Op.  cit.,  p.  26. 


74 


CHEMICAL  ANALYSIS  OF   COAL 


are  made  regularly  every  minute  after  the  first  minute  and  the  first 
reading  taken  after  the  rate  of  fall  becomes  uniform  is  the  last  read- 
ing of  the  combustion  period.  The  readings  are  continued  every 
minute  for  five  or  six  minutes  composing  the  final  period. 

Calculation  of  the  readings:  The  following  plan  shows  the  method 
of  calculating  the  calorimeter  readings  (weight  of  sample  i.oooo 
grams). 


Time    Readings 
p.  m.        °  C. 

23 . 874      o .  0058  rate  of 


i-54 
•55 

.56 
•57 


23.879 

23-885 
28.892 


change  per  minute 
in  preliminary 
period 


.S8(T)  23.897  +  0.00580 


+  O.OO276 


.585      24.160  +  0.00490 


+  o.ooi46 


•59 
.60 

2.01 
.02 
•03 


25.430  +  o.ooo8a 


-  o.ooo66 


26. 280  —  O.OO2Oa 

26.439  —  0.00250 

26.463  —  0.0026° 
26.466  —  0.0026° 


-  0.00236 
—  O.OO266 


—  O.OO266 


26.463° 
23.897 

Observed  temperature 

change 2 . 566 

Thermometer  correction 002 

(Supplied  with  thermometer) 

2.564 
Heat  loss o .  0066 


Water  equivalent 

Total  heat  developed  in  cal- 


ories. .  . 
Correction 


Heat  developed  by  combus- 
tion of  sample  in  calories 


7,670.4 


.04   (t)  26.463 


—  0.0026* 

—  0.0066  algebraic  sum. 


.05  26.460 

.06  26.458 

.07  26.455  ~  0.0026,  rate  of  change  in  final  period 

.08  26.454 

.09  26.450 


Calories 
=      17-9 
=      12.5 
9-9 


Wire  burned  =  11.2  mg 

Titer  (i  c.c.  =  5  cal.)  2.5  c.c 

Sulphur  (o.oi  g.  or  i  per  cent  =  13  cal.)  0.76  per  cent 

Room  temperature  =  24°  C. 

a  Computed  rate  per  minute  of  temperature  change  at  each  reading:     b  Temperature 
correction  for  heat  loss  during  each  interval. 


DETERMINATION  BY   CALORIMETER  75 

Let  A  equal  the  rate  of  change  during  the  preliminary  period  and 
B  equal  the  rate  of  change  during  the  final  period,  then  A-B  will  equal 
the  change  in  rate  during  the  combustion  period. 

Let  T  equal  the  initial  temperature  of  the  combustion  period  and 
/  the  final  temperature  of  the  combustion  period,  then  T-t  equals 
the  apparent  change  in  temperature  during  the  combustion  period. 

Then  -  -  =  the  change  in  rate  per  degree  of  temperature  change 
J.   —  / 

during  the  combustion  period. 

If  the  temperature  readings  during  the  combustion  period  be 
represented  by  t\,  /2,  ^3,  etc.,  or  in  a  general  way  by  /„,  then  the  com- 
puted rate  per  minute  of  temperature  change  at  each  reading  is 
found  by  the  following  formula: 


To  obtain  the  temperature  correction  for  heat  loss  during  each 
interval  multiply  the  mean  of  the  computed  rate  per  minute  of  tem- 
perature change,  for  any  two  readings,  by  the  interval  in  minutes. 
The  algebraic  sum  of  these  corrections  gives  the  total  correction  for 
heat  loss  (e.  g.  —  0.0066°  C.).  This  quantity  is  added  to  the  ob- 
served temperature  change,  and  this  sum  multiplied  by  the  weight 
of  the  water  plus  the  water  equivalent  of  the  apparatus  gives  the 
total  heat  developed. 

Corrections  for  various  factors:  The  observed  temperature  should 
be  corrected  for  errors  in  the  thermometer.  The  correction  for  the 
combustion  of  the  iron  wire  is  1.6  calories  per  milligram.  The  cor- 
rection for  sulphur  burned  to  sulphuric  acid  is  1.3  calories  per  milli- 
gram. The  correction  for  nitrogen  to  aqueous  nitric  acid  is  made 
by  titrating  the  bomb  liquor  with  standard  ammonia  solution  (0.00587 
grams  NH3  per  cubic  centimeter).  This  solution  is  equivalent  to  5 
calories  per  cubic  centimeter. 

Analysis  of  the  calorimeter  washings:  The  calorimeter  is  thor- 
oughly rinsed  out  after  the  combustion  test  is  finished  and  the  wash- 
ings are  titrated  with  standard  ammonia  solution  (0.00587  gram  per 
cubic  centimeter)  to  make  the  acid  correction.  Methyl  orange  is 
used  as  an  indicator.  The  nitric  acid  which  is  present  is  developed 
from  the  nitrogen  in  the  coal  and  from  the  air  imprisoned  in  the 
bomb.  The  solution  also  derives  some  acidity  from  the  sulphur  in 


76  CHEMICAL  ANALYSIS  OF  COAL 

the  coal.  The  sulphur  is  readily  precipitated  by  barium  chloride 
(BaCl2)  as  in  the  Eschka  method  already  described.  Instead  of  the 
ammonia  solution  some  analysts  much  prefer  Stohman's  solution, 
in  which  sodium  carbonate  (Na2CO3)  is  used,  because  of  the  greater 
regularity  of  the  results  obtained  with  it.  One  cubic  centimeter  of 
this  solution  contains  0.003706  gram  sodium  carbonate  and  it  is 
equivalent  to  0.004406  gram  nitric  acid.  One  calorie  of  heat  is 
produced  when  this  acid  is  formed.  Methyl  orange  is  used  as  indic- 
ator. 

It  is  convenient  to  make  the  ammonia  solution  used  of  such  strength 
that  i  c.c.  is  equivalent  to  0.00483  gram  of  nitrogen  because  this 
weight  of  nitrogen  burned  to  nitrogen  pentoxide  (N2O5),  plus  water 
generates  5  calories  of  heat. 

When  nitrogen  burns  to  N2O5  -f  water  1035  calories  of  heat  per 
gram  are  produced. 

The  ammonia  solution  is  made  up  according  to  the  following  equa- 
tion: 

HNO3  +  NH3  =  NH4NO3. 
Since  N  =  14  and  NH3  =  17, 

14  :  17  =  0.00483  gram  :  00587  gram. 

Therefore  0.00587  gram  NH3  is  equivalent  to  0.00483  gram  of  nitro- 
gen which  when  burned  to  nitric  acid  generates  5  calories  of  heat. 
The  standard  solution  contains  5.87  grams  of  NH3  per  liter. 

The  ammonia  used  must  also  neutralize  the  sulphuric  acid  gener- 
ated in  the  bomb  from  the  sulphur  and  the  strength  of  the  ammonia 
solution  in  terms  of  the  sulphur  in  the  form  of  sulphuric  acid  is  de- 
termined by  the  following  equation: 

2NH3  +  H2S04  =  (NH4)2S04 

2NH3  :  S  =  34  :  32  =  0.00587  gram  NH3  :  0.0055  gram  S. 
The  heat  of  combustion  of  the  sulphur  when  converted  into  aqueous 
sulphuric  acid  is  4450  calories  per  gram  of  sulphur  provided  it  is 
burned  in  oxygen  at  high  pressure,  as  it  is  in  the  bomb.  Since  the 
heat  of  combustion  of  the  sulphur  burned  under  a  boiler  in  industrial 
operations  where  it  only  changes  to  sulphur  dioxide  (SO2),  is  reck- 
oned as  2250  calories  per  gram  of  sulphur,  a  correction  must  be  made, 
and  the  figure  employed  is  2200,  or  the  difference  between  the  above 
figures.  Now,  since  i  c.c.  of  the  ammonia  solution  is  equivalent  to 
0.0055  gram  of  sulphur,  0.0055  X  2200  =  12.1  calories.  This  is  the 


DETERMINATION  BY  CALORIMETER  77 

heat  correction  to  be  made  on  the  basis  that  all  the  acidity  in  the 
washings  from  the  bomb  is  due  to  the  presence  of  sulphuric  acid. 
A  correction,  however,  must  be  made  for  the  nitric  acid  as  outlined 
above.  The  difference  12.1  —  5  =  7.1  calories,  and  7.1  -5-  0.0055 
=  1291  calories  per  gram  of  sulphur,  or  practically  13  calories  for 
each  per  cent  of  sulphur  present. 

Standardization  of  the  calorimeter:  A  number  of  methods  have 
been  suggested  for  the  determination  of  the  water-equivalent  of  the 
calorimeter.  One  method  makes  use  of  the  specific  heats  of  the 
various  portions  of  the  apparatus.  Another  is  the  electric  method, 
another  the  mixing  of  portions  of  water  having  different  temperatures,1 
and  still  another  the  employment  of  different  quantities  of  water 
while  generating  the  same  amount  of  heat  in  the  bomb.  None  of 
these  when  considered  from  all  points  of  view  are  as  satisfactory  for 
commercial  operations  as  the  method  where  substances  of  known 
calorific  values  are  used.  The  calorific  value  of  these  substances  is 
determined  with  elaborate  electric  apparatus  by  the  Bureau  of  Stand- 
ards and  samples  may  readily  be  obtained.  The  substances  mostly 
used  are  benzoic  acid,  naphthalene,  and  sucrose.  A  weighed  portion 
of  one  of  these  substances  is  placed  in  the  bomb  and  the  experiment 
carried  out  just  as  for  a  sample  of  coal.  The  weight  of  the  sample 
should  be  such  that  its  calorific  value  will  be  as  nearly  as  possible 
that  of  a  gram  of  coal. 

Method  of  calculating  the  relations  between  "air-dried"  "as  received" 
"moisture-free"  and  "ash-free"  samples:  The  following  system  is 
adopted  in  calculating  percentages  in  the  "air-dried"  sample  to  those 
in  the  "as  received"  sample: 

1  Bownocker,  J.  A.,  Lord,  N.  W.,  and  Somermeier,  E.  E.,  Coals  of  Ohio.  Ohio  State 
Geol.  Survey,  Bull.  9,  p.  331,  1908. 


CHEMICAL  ANALYSIS  OF  COAL 

"Air-dried"  condition 


"As  received"  condition 
ioo  —  air-drying  loss 


Moisture  at  105    ^.  multiplied  oy 

Volatile  matter 
Fixed  carbon 
Ash 
Sulphur                             "          " 
Hydrogen 

Carbon                             "          " 
Nitrogen                          "          " 
Oxygen                            " 

Calorific  value                 "          " 

Calculating  percentages  in  the 
1  '  moisture-free  '  '  sample  . 

"Air-dried"  condition 
Volatile  matter  multiplied  by 

Fixed  carbon 
Ash 

IOO 

air-drying  loss              =  moisture 
ioo  —  air-drying  loss  i_*:i.._ 

ioo  -  air-drying  loss 

IOO 

ioo  —  air-drying  loss 

IOO 

ioo  -  air-drying  loss 

IOO 

ioo  —  air-drying  loss  , 

IOO 

air-drying  loss              _        , 

9 
ioo  -  air-drying  loss  _ 

IOO 

ioo  -  air-drying  loss  _     h 

IOO 

ioo  —  air-drying  loss   , 

1 
8  (air-drying  loss) 

9 
ioo  —  air-drying  loss          ,     .-        , 

"  air-dried"  sample  to  those  in  the 

"Moisture-free"  condition 
^~  volatile  matter 

ioo  —  moisture 

IOO 

ioo  —  moisture 
—  —  ash 

ioo  —  moisture 

ioo  —  moisture 
—  hydrogen 

Hydrogen  (      9  moisture) 
Carbon 

ioo  —  moisture 

IOO 

,  .  _      ,  rrr  carbon 

ioo  —  moisture 

IOO 

ioo  —  moisture 

IOO 

'•  —  oxygen 

Uxygen  ^      -§-  moisture,; 
Calorific  value               "         * 

ioo  —  moisture 

ioo  —  moisture 

(i  calorie  =1.8  B.t.u.) 


CALCULATION  OF  THE  CALORIFIC  VALUE  OF  COAL      79 

To  calculate  the  analyses  to  an  "ash-free"  and  " moisture-free" 
basis  use  as  denominator  100  —  (moisture  +  ash)  instead  of  "  100 
—  moisture."  ~~»— 

Calculation  of  the  Calorific  Value  of  Coal  from  the  Analysis 

The  formula  of  Dulong  is  recognized  as  the  most  satisfactory  for- 
mula so  far  devised  for  determining  the  calorific  value  from  the  an- 
alysis. It  has,  however,  been  modified  in  a  number  of  ways.  It 
is  usually  expressed  as:  Calorific  value  in  calories  per  gram  =  8080 

C  -f-  34,460  ( H  —  —  J  +  S  2250,  where  C,  H,  O,  and  S,  respectively, 

indicate  the  weights  of  the  carbon,  hydrogen,  oxygen,  and  sulphur. 
This  formula  is  not  quite  correct  in  view  of  the  figures1  lately  ob- 
tained for  the  heating  value  of  carbon,  which  should  be  approximately 
8100  C  instead  of  8080  C,  and  34,500  is  a  better  figure  to  employ  than 
34,460. 

To  avoid  the  necessity  of  analyzing  the  coal  for  hydrogen  Parr2 
uses  the  formula  8080  C  +  34,500  "H"  +  2250  S  in  which  "H"  rep- 
resents the  available  hydrogen  in  the  coal,  or  hydrogen  not  combined 
with  oxygen  to  form  water,  and  it  is  derived  from  a  curve  which  is 
based  on  the  principle  that  the  hydrogen  is  united  with  some  of  the 
volatile  carbon.  He  considers  that  the  value  for  hydrogen  so  de- 
rived and  used  in  Dulong's  formula  will  produce  results  practically  as 
satisfactory  as  those  obtained  from  the  original  formula,  and  they 
are  obtained  much  more  readily. 

The  calorific  value  from  the  proximate  analysis:  If  the  calorific 
value  could  be  calculated  from  the  proximate  analysis  a  great  advance 
would  be  made  over  Dulong's  formula.  What  appears  to  be  a  sat- 
isfactory method  for  computing  the  calorific  value  of  certain  coals 
from  the  proximate  analysis,  has  been  suggested  by  Goutal3  as  a 
result  of  experiments  on  over  600  specimens  of  various  kinds  of  coal. 
He  used  the  following  formula: 

P  =  82  C  +  a  V  in  which 

P  =  the  number  of  calories  in  a  gram  of  fuel, 

C  =  the  percentage  weight  of  fixed  carbon,  and 

1  Richards,  Metallurgical  calculations,  Part  I. 

2  Parr,  S.  W.,  Op.  cit,  p.  64. 

3  Goutal,  M.,  Sur  le  pouvoir  calorifique  de  la  houille.    Compt.  Rend.,  Vol.  135,  p. 
477,  1902 


8o 


CHEMICAL  ANALYSIS  OF  COAL 


V  =  the  percentage  weight  of  the  volatile  matter;  while 

a   =  a  coefficient  which  varies  with  the  percentage  of  volatile 

matter,  V,  in  the  pure  coal. 
a  is  found  from  a  curve   (Fig.  13).     This  curve  is  constructed  by 


145 

\f 

140 

135 
110 

X 

s 

( 

125 
120 
115 
110 
105 
100 
95 
90 
85 

"X 

"V 

^ 

^ 

•- 

'  — 

--*. 

— 

•  —  ^ 

-*^. 

•^ 

^^ 

^ 

^ 

•x 

5  10  15  20  25  30  35 

Fig.  13.  —  Goutal's  curve  for  the  determination  of  the  calorific  value  of  coal 
from  the  proximate  analysis. 

taking  the  values  for  V  as  the  abscissae  and  the  values  for  a  as  the 
ordinates.     V  is  found  from  the  formula 


and  a  was  found  as  a  result  of  a  vast  number  of  analyses  which  were 
made  during  this  investigation.  In  the  anthracites  a  =  100,  a  con- 
stant. 

The  values  5,  10,  15,  20,  25,  30,  35,  38,  and  40  per  cent  for  volatile 
matter  in  the  pure  fuel  (V)  give  the  corresponding  figures  for  a  as 
follows:  145,  130,  117,  109,  103,  98,  94,  85,  and  80  per  cent  respec- 
tively. 

For  coals  with  a  value  for  V  between  5  and  35  per  cent  the  variation 
between  the  results  given  by  this  method  and  those  given  by  the 
calorimeter  rarely  vary  more  than  i  per  cent.  The  value  may  reach 
2  per  cent  in  some  anthracites  and  in  weathered  coals  or  lignites,  and 
for  these  the  calorimeter  method  is  the  only  accurate  means  of  de- 
termining their  calorific  value. 

The  following  table  from  Carnot  shows  how  closely  the  results 
obtained  by  Goutal's  formula  correspond  to  those  obtained  from 
Dulong's  formula  and  the  calorimeter.  They  are  in  every  case  closer 
to  the  calorimetric  figures  than  are  those  from  Dulong's  formula. 


CALCULATION  OF  THE  CALORIFIC  VALUE  OF  COAL 


81 


CALORIFIC 

VALUE  BY  VARI 

ous  MEANS 

Fixed 
carbon 

Volatile 
matter 

Calorimetef 

From    Du- 
long's  for- 
mula 

FromGoutal's 
formula 

Anthracite  of  Pennsyl- 
vania   

Q7  .O 

3  .0 

8256 

8462 

8380 

Anthracite      coal      of 
Keboa 

Q4.  8 

52 

8<?32 

8<>28 

8<2Q 

Anthracite  coal  of  Creu- 
sot 

8q  6 

IO   4. 

8687 

8704 

8680 

Semi-fat  coal  of  Angers 
Fat  coal  of  Porter  

85-9 
80.7 

I4.I 
19.3 

8656 
8667 

8750 
8382 

8722 
8740 

Fat  coal  of  Ronchamp.  . 
Gas  coal  of  Bethune  
Gas  coal  of  Montram- 
bert    • 

76.8 
69.6 

6s    7 

23.2 
30-4 

•2  A      *} 

8797 

8668 
8^08 

8678 
8654 

8-1O7 

8702 
8671 

86l2 

CHAPTER  IV 
VARIETIES  AND  RANKS   OF   COAL 

Introduction 

The  various  classifications  of  coal  which  have  been  suggested  are 
discussed  in  another  chapter.  There  are,  however,  certain  varieties 
recognized  almost  universally  in  science  and  commerce  which  should 
be  described  in  detail  before  a  comprehensive  description  of  the  less 
familiar  classifications  can  be  given.  These  varieties  are  not  sharply 
separated  and  they  grade  into  one  another,  so  that  in  describing 
them  the  proportions  of  their  constituents  must  be  stated  as  varying 
within  wide  limits.  Two  coals  with  a  certain  percentage  of  fixed 
carbon  may  have  very  different  calorific  properties  owing  to  the  fact 
that  the  moisture  or  the  ash  may  vary  considerably,  and  consequently 
if  one  constituent  be  chosen  as  a  standard  the  others  do  not  necessarily 
agree.  An  attempt  has  been  made,  therefore,  to  give  the  limits  of 
variation  as  well  as  the  average  properties  of  these  different  varieties 
as  they  have  been  recognized  by  many  writers  from  numerous  coun- 
tries. The  ideal  manner  of  presenting  all  the  constituents  other  than 
moisture  and  ash,  would  be  on  a  "moisture-free"  and  " ash-free" 
basis,  but  since  the  analyses  selected  have  not  been  so  recorded  they 
have  not  been  computed  on  this  basis  in  the  following  figures  unless 
it  be  so  stated  in  the  text. 

Since  it  is  so  generally  admitted  that  all  coal  has  been  derived  from 
peat  in  some  form  and  that  it  has  arrived  at  its  present  state  as  the 
result  of  various  geological  processes,  peat  is  briefly  described  with 
the  varieties  of  coal.  It  is  not  regarded  as  a  variety  of  coal,  but 
rather  as  an  incipient  stage  in  the  formation  of  that  substance. 

Peat  (Fr.  Tourbe,  Ger.  Torf).  —  Peat  is  an  accumulation  of 
vegetal  matter  which  has  suffered  varying  degrees  of  disintegration 
and  decomposition,  and  it  contains  a  high  percentage  of  water  and 
oxygen.  It  varies  in  physical  character  from  a  distinctly  fibrous  and 
woody,  light-brown  material  to  a  dark-brown  and  black  jelly-like 
substance.  There  are  all  gradations  from  peat  to  muck  in  which 

82 


PEAT  83 

mineral  matter  becomes  so  abundant  as  to  prevent  its  free  burning. 
Although  it  may  be  cut  from  the  bog  in  blocks  peat  is  seldom  suffi- 
ciently compact  to  make  a  good  fuel  without  compressing. 

The  composition  of  peat  is  illustrated  by  the  following  figures. 
Water  in  original  samples  from  different  parts  of  the  bog  is  62.98  to 
90.12  per  cent,  usually  80  to  90  per  cent.  In  a  large  number  of 
analyses  of  dried  specimens  from  various  countries  the  following 
variations  and  averages  in  composition  are  shown: 


Variations 

Carbon 37 . 15-66 . 55  per  cent 

Hydrogen 4 . 08-10 . 39        " 

Oxygen 18. 59-42 .63        " 

Nitrogen o .  77-  3 . 10        " 

Fixed  carbon 10.39-33 .91        " 

Volatile  matter 43 .38-73 .60        " 

Ash 1.05-32.95        " 


Average 
52.83  per  cent 

5-97  " 
33-12  « 

1-34  " 
23-59  " 
60. 18  " 

9.58        " 


Sulphur  is  often  as  low  as  one-tenth  of  i  per  cent  and  it  is  usually 
below  i  per  cent,  but  it  may  rise  higher  in  pyritiferous  types.  The 
calorific  value  varies  from  5500  to  10,000  B.t.u.  in  air-dried  samples. 


Fig.  14.  —  Branch  of  tree  altered  to  lignite  but  preserving  the  original 
markings.     From  the  coast  of  Alaska.     (Collected  by  W.  R.  Crane.) 

Dopplerite:  This  is  a  variety  of  peat,  found  chiefly  in  Styria  but 
also  occurring  elsewhere  in  Europe,  whose  composition  shows  it  to 
be  highly  acid.  An  analysis  by  Schrotter  shows  that  it  contains 

Carbon 48 . 06  per  cent 

Hydrogen 4-98        " 

Oxygen 40 . 07        " 

Nitrogen i .  03        " 

Ash 5.86        " 

It  is  amorphous  and  in  the  fresh  state  is  elastic  like  rubber.     Its 


84  VARIETIES  AND  RANKS  OF   COAL 

luster  is  greasy  and  its  specific  gravity  is  1.089.  It  burns  with  little 
or  no  flame  and  emits  an  odor  like  peat. 

Lignite  and  brown  coal  (Fr.  Lignite,  Ger.  Braunkohle). —  There 
seems  to  be  no  definite  record  of  the  first  use  of  the  term  lignite. 
It  is  a  French  word  and  may  possibly  have  arisen  from  the  term 
Lithanthrax  ligneus  which,  according  to  Hausmann1  was  used  by 
Wallerius2  for  the  distinctly  woody  type  of  brown  coal.  It  was 
used  by  Brongniart3  as  early  as  1807  and  it  is  generally  found  in  all 
French  works  since  that  time.  The  German  word,  Braunkohle  was 
used  in  different  ways  by  Karst,4  Neuss,5  and  Blumenbach6  about 
the  beginning  of  the  nineteenth  century. 

In  America  the  terms  lignite  and  brown  coal  have  come  to  be  used 
interchangeably  because  both  the  amorphous  and  the  xyloid,  or 
woody  types  may  be  brown  in  color  and  may  have  similar  chemical 
properties  and  uses.  The  two  types  grade  into  each  other  so  that  no 
sharp  distinction  can  be  made  between  them.  In  recent  years,  how- 
ever, the  United  States  Geological  Survey  has  decided  to  adopt  the 
term  subbituminous  coal  for  the  compact,  so-called  "black  lignite" 
and  to  restrict  the  term  lignite  to  the  lower  grade  brown  coal  which  is 
usually,  but  not  always  more  or  less  woody  and  on  drying  splits  up 
into  slabs.7  (Plate  III,  Fig.  i.)  The  distinction  is  thus  made  on 
the  basis  of  color.  The  composition  of  lignite  or  brown  coal,  as  these 
terms  are  used  in  various  countries,  is  indicated  by  the  following 
figures  compiled  from  numerous  analyses  of  this  coal  from  almost 
all  parts  of  the  world : 

Variation  Average 

Moisture o .  75-43 .  oo  per  cent  14.42  per  cent 

Volatile  matter 27 . 00-53  •  °°       "  4°  •  7^       " 

Fixed  carbon 16 . 00-51 .00       "  36 . 37 

Ash 2.60-42.00       •'  9.32 

Sulphur 0.16-9.00       "  i  .14       " 

Hydrogen . 5 . 14       " 

Carbon 58.14       " 

Nitrogen i .  05       " 

Oxygen 25 . 17       " 

Hausmann,  J.  F.  Ludw.,  Handbuch  der  Mineralogie,  Vol.  i,  p.  79,  1813. 
Wallerius,  J.  G.,  Systema  Mineralogicum,  Vol.  2,  p.  98,  1775. 
Brongniart,  Alexandre,  Traite  61ementaire  de  Mineralogie,  Tome  2,  1807. 
Karst,  Mineralogische  Tabellen  58,  1800. 
Neuss,  Min.  II,  3,  154. 

Blumenbach,  Handbuch  Der  Naturgeschichte  I,  660. 

Campbell,  M.  R.,  A  practical  classification  of  low-grade  coals.    Econ.  Geology,  Vol. 
3,  p.  134,  1908. 


PLATE  III. 


Fig.  i.  —  North  Dakota  lignite  showing  characteristic  fracture  and  xyloid 

texture. 


Fig.  2.  —  Bituminous  coal  showing  characteristic  cubical  fracture.  85 


86  VARIETIES  AND    RANKS  OF   COAL 

The  calorific  value  of  lignite,  undried  as  received  from  the  mine, 
is  5500-7000  B.t.u.  —  moisture-and-ash-free,  10,000-12,000  B.t.u. 
The  specific  gravity  is  0.5  to  1.30.  It  colors  brown  a  solution  of 
potash.  Some  lignites  in  France  are  so  high  in  pyrite  that  they  can 
be  used  in  the  manufacture  of  iron  sulphate  and  alum,  and  certain 
earthy  varieties,  known  as  terre  d'ombre  or  ombre  de  Cologne,1  are  used 
for  coloring  matter. 

Dysodile  (Houille,  or  lignite  papyracee):  This  is  a  laminated  lig- 
nite high  in  siliceous  ash.  The  color  is  a  yellow  to  greenish-gray,  the 
specific  gravity  1.14  to  1.25.  It  burns  readily  with  a  bright  flame 
and  gives  off  an  odor  like  asafetida.  The  ash  has  been  found  to  con- 
tain abundant  shells  of  diatoms.  An  analysis  by  Church2  shows 
the  following  composition,  ash  free: 

Sulphur 2.35  per  cent 

Hydrogen 10 . 04       " 

Carbon 69 . 01       " 

Nitrogen i .  70       " 

Oxygen 16 . 90       " 

It  occurs  in  Tertiary  formations,  and  is  found  in  limestone  in  Sicily 
and  in  lignite  in  Germany  and  the  Central  Plateau  of  France. 

Subbituminous  coal.  —  This  term  has  been  officially  adopted  by 
the  United  States  Geological  Survey  to  include  the  glossy  black  coal 
which  grades  downward  in  properties  from  bituminous  to  lignite  but 
which,  as  a  rule,  is  of  a  considerably  higher  grade  than  the  woody  or 
ligneous  type.  It  includes  the  black  lignite  and  since  it  may  be  lig- 
neous in  texture  it  can  in  some  cases  be  distinguished  from  brown  coal 
in  the  field  only  by  its  black  color,  while  it  is  separated  from  bituminous 
coal  above  by  its  mode  of  weathering.  According  to  Campbell.3 
it  parts  along  a  surface  nearly  parallel  to  the  bedding  and  thus  breaks 
up  into  thin  slabs,  or  it  checks  irregularly  and  does  not  disintegrate 
into  cubes  after  the  manner  of  bituminous  coal.  (Plate  IV,  Fig.  i.) 
The  fracture  is  sometimes  conchoidal.  It  often  has  a  distinctly 
pitchy  luster  and  is  therefore  sometimes  called  Pechkohle  (pitch  coal) 
by  the  Germans.  Analyses  of  samples  of  this  variety  of  coal  as  it  is 

1  Moissan,  Traite"  de  chimie  min^rale,  Vol.  2,  p.  356,  1905. 

2  Church,  A.  H.,  Dysodile.     Chem.  News,  Vol.  34,  p.  155,  1876. 

3  Op.  cit. 


BITUMINOUS   COAL  87 

known  in  the  United  States  show  the  following  variations  in  per- 
centage composition,1 

Moisture i  •  94~4Q .  58  per  cent 

Volatile  matter 7 •  50-70.86       " 

Fixed  carbon 18 . 00-83  •  °o       " 

Ash 2.06-55.40       " 

Sulphur 0.15-8.65       " 

Hydrogen i .  76-  6 . 98 

Carbon 30.68^86.85 

Nitrogen o .  49-  2.13 

Oxygen 2 . 80-52 . 18 

Air-drying  loss o .  80-28 .  oo 

Calorific  value 6205-14,843  B.t.u. 

Good  grades  of  this  coal  have  a  calorific  value  of  8000  to  10,000  B.t.u. 

Bituminous  coal  (Fr.  Houille,2  Ger.  Schwarzkohle3).  —  The  term 
bituminous  has  evidently  been  handed  down  from  the  earliest  writers 
on  mineralogy  because  they  frequently  spoke  of  the  volatile  ma- 
terials given  off  this  type  of  coal  on  distillation,  as  bitumen.  Wal- 
lerius  called  this  coal  Bitumen  lapideum.  Among  some  modern 
writers  there  is  a  tendency  to  discard  bituminous  for  the  term  humic 
since  the  coal  lacks  true  bitumen  in  important  amounts  and  contains 
a  large  percentage  of  humic  acid. 

Bituminous  coal  burns  with  a  long  yellowish  flame  and  gives  off 
a  suffocating  bituminous  odor.  It  is  more  or  less  laminated  as  a  rule, 
and  the  luster  of  the  different  layers  varies  greatly.  It  may  be  resin- 
ous, silky,  pitchy,  or  dull  and  earthy.  It  soils  the  fingers  when 
handled.  The  color  varies  from  pitch-black  to  dark  gray.  The 
fracture  may  be  irregular  and  somewhat  splintery  but  it  is  almost 
always  roughly  cubical.  (Plate  III,  Fig.  2.)  It  is,  as  a  rule, 
conchoidal  in  cannel  coal. 

There  are  several  types  of  bituminous  coal.  These  include  Caking 
and  Non-caking  coal  —  the  latter  including  the  Cherry  and  Splint 
coals  of  England,  —  Cannel  coal  and  its  related  types,  Torbanite  and 
Boghead. 

Caking  or  coking  coal:  This  coal  has  the  property  of  softening  and 
running  together  into  a  pasty  mass  at  the  point  of  incipient  decom- 

1  Lord,  N.  W.,  and  others,  Analyses  of  coals  in  the  United  States.     U.  S.  Bur.  Mines, 
Bull.  22,  1912. 

2  De  Lisle,  Vol.  2,  p.  590,  1783.     Hauy,  Trait<§  de  mineralogie,  Vol.  3,  p.  316,  1801. 
8  Hausmann,  Op.  cit.,  p.  73. 


88  VARIETIES   AND   RANKS  OF  COAL 

position  and  then  at  higher  temperatures  giving  off  its  volatile  con- 
stituents as  bubbles  of  gas.  There  remains  a  hard,  gray,  cellular 
mass  called  coke  (Fr.  Coke,  Ger.  Coaks).  While  there  is  no  chemical 
or  simple  physical  test  which  will  distinguish  coking  coals  in  all  cases, 
there  are  some  tests  which  will  usually  indicate  their  coking  proper- 
ties. White1  states  that  practically  all  coals  with  H  :  O  ratios  of  59 
per  cent  or  over  seem  to  possess  the  quality  of  fusion  and  swelling 
necessary  to  good  coking.  Most  with  ratios  down  to  55  will  make 
coke  of  some  kind,  while  a  few  with  ratios  as  low  as  50  coke  in  the 
beehive  oven,  though  very  rarely  producing  a  good  article.  Coals 
changing  to  anthracite,  the  weathered  coals,  and  the  coals  of  the 
boghead  —  cannel  group  show  considerable  variation  from  this  rule. 
It  has  been  shown,  also,  that  the  solubility  of  coal  in  aniline  may  be 
used  as  an  indication  of  coking  properites.  Vignon2  says  that  the 
coke  given  by  the  coal  insoluble  in  aniline  is  powdery  and  that  of 
the  coal  soluble  in  aniline  is  agglomerated  and  swollen. 

A  simple  and,  in  many  cases,  a  satisfactory  test  is  that  known  as 
the  agate  mortar  test.  Coals  which  coke,  when  rubbed  with  a  pestle 
in  an  agate  mortar,  cling  to  the  sides  of  the  mortar  while  the  non- 
coking  coals  do  not.3 

Non-caking  or  non-coking  coal:  This  coal  may  resemble  the  coking 
coal  in  all  outward  appearances  but  in  composition  it  differs  in  the 
ratio  of  the  hydrogen  to  the  oxygen  and  it  does  not  cling  to  the  sides 
of  an  agate  mortar  when  rubbed  with  the  pestle.  It  burns  freely 
without  softening  and  it  leaves  a  powdery  mass  instead  of  a  strong 
cellular  mass.  The  Cherry  coal,  so  well  known  in  England,  is  a 
variety  of  the  non-coking  coal.  It  received  its  name  because  of  its 
fine  luster.  It  is  usually  velvet-black  in  color,  is  brittle  and  crumbles 
rather  readily.  Splint  coal  or,  as  it  is  sometimes  called,  "Slate 
coal,"  is  also  an  English  name  for  a  variety  of  non-coking  coal.  It  is 
black  and  as  a  rule  it  has  a  resinous  and  glistening  luster,  but  often 
it  is  dull  and  contrasts  with  the  brilliant  luster  of  the  Cherry  coal. 
It  fractures  in  two  directions,  the  longitudinal  break  being  curved 
and  slaty  and  the  transverse  uneven  and  splintery. 

1  White,  David,  The  effect  of  oxygen  in  coal.     U.  S.  Geol.  Survey,  Bull.  382,  1909. 

2  Vignon,  Leo,  Sur  les  dissolvants  de  la  houille.     Compt.  Rend.,  Tome  158,  pp.  1421- 
1424,  1914. 

3  Pishel,  M.  A.,  A  practical  test  for  coking  coals.    Econ.  Geology,  Vol.  3,  pp.  265-275, 
1908. 


CANNEL  COAL  89 

The  composition  of  bituminous  coal,  as  it  has  been  recognized  by 
different  writers  in  various  countries  is  as  follows: 

Variation  Average 

Moisture 0.04-34.33  per  cent  2 . 50  per  cent 

Volatile  matter 8.63-64.31        "  32.00       " 

Fixed  carbon 26.49-80.60  55.00 

Ash 0.28-45.00       "  10.00        " 

Sulphur 0.0012-10.5      "  0.80       " 

Hydrogen 1.00-8.80       "  4.80       " 

Carbon 44.00-85.30        "  74.00       " 

Nitrogen 1.00-9.20       "  1.30       " 

Oxygen 0.95-46.90       "  7.00       " 

Calorific  value 6840-15,169  B.t.u.  13,200  B.t.u. 

The  specific  gravity  varies  from  1.15  to  1.5,  with  an  average  of  1.3. 
A  good  average  for  the  percentage  composition  and  calorific  value  of 
the  bituminous  coals  collected  in  the  United  States  between  the 
years  1904  and  19 lo1  is  as  follows: 

Moisture 2 .00-10.00  per  cent 

Volatile  matter 25 .00-40.00       " 

Fixed  carbon 45 . 00-65  •  °°       " 

Ash 5.00-12.00       " 

Sulphur 0.50-  2.00       " 

Hydrogen 4 . 50-  6 .  oo       " 

Carbon 60. 00-80.  oo       " 

Nitrogen o. 80-  2 . oo       " 

Oxygen 7 . 00-20 .  oo       " 

Calorific  value 12,000-14,500  B.t.u. 

Cannel  coal.2  —  This  coal  was  originally  known  as  candle  coal,  but 
the  term  cannel  was  employed  by  the  earliest  mineralogists.  Kirwin3 
describes  this  coal,  along  with  Kilkenny  coal,  as  dull  black  in  color 
and  with  conchoidal  fracture  when  broken  transversely.  It  burns 
with  a  bright  lively  flame  and  in  some  cases  it  may  be  kindled  by  the 
application  of  a  match  owing  to  the  large  percentage  of  highly  volatile 
constituents  which  it  contains.  This  property  gave  rise  to  the  name 
candle  coal.  A  variety  of  Scotch  cannel  which  produces  a  marked 
crackling  sound  has  been  called  parrot  coal  and  Dana4  mentions  a 
variety  from  South  Wales  known  as  horn  coal  because,  on  burning, 
it  emits  an  odor  as  of  burning  horn. 

1  U.  S.  Bur.  of  Mines,  Bull.  22. 

2  Ashley,  G.  H.,  Cannel  coal  in  the  United  States,  U.  S.  Geol.  Survey,  Bull.  659,  1917. 

3  Kirwin,  Richard,  Elements  of  mineralogy.     P.  215,  1784. 

4  Dana,  E.  S.,  A  system  of  mineralogy.    6th  ed.,  p.  1022,  1895. 


VARIETIES   AND    RANKS   OF   COAL 


Cannel  coal  is  generally  described  as  a  non-coking  bituminous 
type,  but  it  is  just  within  the  boundary  of  a  special  group,  the  mem- 
bers of  which  are  char- 
acterized by  a  higher 
percentage  of  volatile 
oils  and  gases  than  that 
found  in  ordinary  bitu- 
minous coal.  To  this 
group  Rogers  applied 
the  term  hydrogenous 
or  gas  coals,1  while  Po- 
tonie2  considers  most 
of  them  as  sapropelic 
types.  Cannel  un- 
doubtedly consists 
chiefly  of  the  spores  of 
plants  or  canneloid 
and,  as  a  result,  differs 
FIG.  15.  —  Photomicrograph  of  section  of  cannel  markedly  from  ordin- 

coal  consisting  almost  entirely  of  flattened  spores.  coal    in    the    char 

(Photo  by  E.  C.  Jeffrey.)  " 

acter  of  the  materials 

which  compose  it.  (Fig.  15.)  Beginning,  therefore,  with  a  different 
type  of  vegetal  matter  it  is  possible  to  have  it  pass  through  the 
stages  corresponding  to  brown  and  to  bituminous  coal,  still  retaining 
its  canneloid  character.  Its  average  composition  is  illustrated  by 
the  following  analysis  of  Kentucky  cannel: 

Moisture 2.36  per  cent 

Volatile  matter 48 . 40 

Fixed  carbon  38 . 75 

Ash 10. 49 

Sulphur i .  20 

Hydrogen 6 . 47 

Carbon 71-98 

Nitrogen i .  16 

Oxygen 8 . 70 

Calorific  value i3>77°  B-t.u. 

The  specific  gravity  varies  from  1.2  to  1.3. 

1  Rogers,  H.  D.,  Geology  of  Pennsylvania.     Vol.  2,  p.  990,  1883. 

2  Potoni6,  H.;  Die  Enstehung  der  Steinkohle  und  der  Kaustobiolith  iiberhaupt,  wie 
des  Torfes,  der  Baunkohle,  des  Petroleums,  u.s.w.,  5th  ed.  1910. 


CANNEL   COAL  91 

Torbanite:  This  is  a  variety  of  the  boghead  coals  and  it  is  named 
from  Torbane  Hill  in  Scotland  where  it  has  been  mined  for  many 
years.  It  differs  so  much  from  ordinary  coal  that  a  prominent  law- 
suit was  carried  through  the  Scottish  courts  about  the  middle  of  the 
last  century  to  determine  whether  the  mining  of  the  rock  was  governed 
by  the  laws  controlling  mineral  or  coal  deposits.  The  trial  was 
settled  in  favor  of  the  latter.  Like  the  other  bogheads  it  is  charac- 
terized by  a  very  high  percentage  of  volatile  constituents  including 
illuminating  and  lubricating  oils,  paraffin,  and  large  quantities  of 
illuminating  gases,  running  from  14,000  to  18,000  cubic  feet  per  ton. 
There  is  a  difference  of  opinion  concerning  its  origin,  some  regarding 
it  as  derived  from  spores,  others  from  algae,  and  it  is  often  described 
as  a  variety  of  cannel  coal.  The  evidence  is  strongly  in  favor  of  the 
origin  from  spores  rather  than  from  algae.  It  is  closely  related  to  the 
kerosene  shales  and  bituminous  schists.  Its  color  is  dark  brown,  its 
surface  dull  and  lusterless.  The  fracture  is  irregular  to  subcon- 
choidal.  According  to  Dana1  the  hardness  is  2.25  and  the  specific 
gravity  1.17  to  1.2.  Analyses  quoted  by  the  same  authority  show 
that  the  composition  is  approximately  as  follows,  with  ash  excluded: 

Hydrogen n  .48  per  cent 

Carbon 81.15        " 

Nitrogen 1.37        ;< 

Oxygen 6 .  oo       •' 

The  ash  runs  about  20  per  cent.     It  is  much  higher  in  hydrogen  than 
any  ordinary  type  of  coal. 

Byerite:  This  is  a  term  applied  by  Mallett2  to  a  so-called  mineral 
coal,  somewhat  resembling  Torbanite  but  differing  from  it  in  not 
crackling  in  the  fire,  in  being  heavier  —  specific  gravity  1.323  —  and 
in  melting  and  intumescing  when  heated.  It  gives  a  large  amount 
of  gas  and  tarry  oils,  about  30  per  cent  more  than  English  cannel. 
An  analysis  gave  the  following  results  —  moisture  6.02  per  cent; 
volatile  matter  (gas  and  tarry  oils)  39.95  per  cent;  fixed  residue, 
consisting  of  coke  and  ash  54.03  per  cent.  The  coke  is  a  true  coke 
but  resembles  the  residue  from  the  distillation  of  sugar  and  is  too 
porous  and  crumbling  to  support  a  furnace  burden.  It  is  jet-black 
in  color  but  gives  a  brown  powder  which  does  not  color  a  potash  solu- 
tion brown.  It  is  insoluble  in  carbon  bisulphide,  ether,  or  turpentine. 

1  Op.  cit.,  p.  1022. 

2  Mallett,  E.  J.,  On  Middle  Park  mineral  coal.    Am.  Jour,  of  Sci.,  Vol.  9,  p.  146, 1875. 


92  VARIETIES   AND   RANKS  OF  COAL 

Semibituminous  coal.  —  H.  D.  Rogers1  adopted  this  term  for  coal 
containing  from  n  to  18  per  cent  volatile  matter  and  to  include  what 
has  been  called  dry  bituminous  coal,  as  opposed  to  the  group  of  fat 
coals  including  caking  coal,  cherry  coal,  and  splint  coal.  This  type  is, 
caking  and,  non-caking.  In  spite  of  the  fact  that  on  heating  it  softens 
and  swells  into  a  coke,  this  coke  does  not  always  agglutinate  or  cohere. 
Although  the  term  is  quite  widely  used  in  the  United  States,  it  seems 
a  little  unfortunate  in  view  of  the  fact  that  the  prefix  semi  conveys  the 
idea  that  it  should  be  a  little  below  bituminous  coal  in  the  ascending 
scale  from  peat  to  anthracite,  and  it  does  not  harmonize  with  the  use 
of  the  term  semianthracite.  The  term  superbituminous  might  have 
been  suggested  as  a  more  appropriate  one.  Rogers  did  not  give  any 
detailed  description  of  this  type  of  coal  but  various  analyses  from 
fields  throughout  the  United  States2  show  the  varying  proportions 
of  the  following  constituents  and  their  average  in  a  good  quality  of 
this  variety  of  coal: 

Variation  Average 

Moisture o .  78-  8 . 99  per  cent         2 .  oo-  4 .  oo  per  cent 

Volatile  matter 7 . 40-23 .84  14 . 00-18 .  oo       " 

Fixed  carbon 57. 11-80.89  70.00-80.00       " 

Ash 1.80-34.15  4.00-8.00       " 

Sulphur o .  44-  6 . 47  o .  50-  i .  20        " 

Hydrogen 3 .34-5.17  4.00-5.00       " 

Carbon 51.23-85.54  76.00-82.00       " 

Nitrogen 0.81-1.82  1.00-1.50       " 

Oxygen 3.38-13.70  4.50-6.50 

Calorific  value 8386-14,814  B.t.u.  14,000-15,000  B.t.u. 

Semianthracite.  —  This  name  was  adopted  by  Rogers3  at  the  same 
time  as  the  term  semibituminous,  to  cover  the  coal  between 
semibituminous  and  anthracite.  He  describes  it  as  possessing 
to  a  lesser  degree  the  properties  characteristic  of  anthracite.  The 
conchoidal  fracture  is  not  so  well  developed  as  in  anthracite,  and  the 
cleats  are  more  numerous.  It  crumbles  more  readily  in  the  fire  and 
owing  to  a  greater  percentage  of  volatile  matter  it  kindles  more 
readily  than  anthracite  and  emits  a  small  amount  of  yellow  flame 
when  ignited.  Owing  to  more  rapid  consumption  its  efficiency  is 
greater  than  that  of  anthracite  for  certain  purposes.  The  volatile 

1  Rogers,  H.  D.,  Geology  of  Pennsylvania,  pp.  988-990,  1858. 

2  Analyses  of  coals  in  the  United  States.     Bur.  of  Mines,  Bull.  22,  1912. 

3  Op.  cit. 


PLATE  IV. 


FIG.  i.  —  Subbituminous  coal  showing  irregular  fracture. 


FIG.  2.  —  Pennsylvania  anthracite  showing  typical  conchoidal  fracture. 


(9-0 


94  VARIETIES   AND   RANKS   OF   COAL 

matter  varies  from  6  to  1 1  per  cent  and  averages  from  7  to  8  per  cent. 
The  specific  gravity  is  about  1.4.  Analyses  of  this  type  of  coal  from 
the  United  States1  indicate  the  following  range  in  composition: 

Moisture i .  96-  7 . 94  per  cent 

Volatile  matter 6.81-32 .46 

Fixed  carbon 58 .  24-82 .  oo 

Asn 4.33-14.50 

Sulphur 0.57-  4 . 05 

Hydrogen 3.69-  4.81 

Carbon 72 . 43-80 .  oo 

Nitrogen 0.51-  1.45 

Oxygen 5 . 46-10 . 02 

Calorific  value 12,460-14,184  B.t.u. 

A  proximate  analysis  of  a  good  grade  of  this  coal  is  represented  by  the 
following : 

Moisture i .  94  per  cent 

Volatile  matter 9 . 95        " 

Fixed  carbon 79 .  oo       " 

Ash 8.80       " 

Sulphur o .  29       " 

Anthracite  (Fr.  Anthracite,  Ger.  Glanzkohle) .  —  The  first  use  of 
this  term  among  mineralogists  is  ascribed  to  Hauy,2  although  An- 
thrazit  may  have  been  employed  by  Karst3  ten  years  earlier.  In 
America  this  coal  is  frequently  known  as  hard  coal,  and  in  Wales  as  culm 
or  stone  coal.  It  is  characterized  by  an  iron-black  color,  and  dull  to 
brilliant,  and  even  submetallic  luster.  It  does  not  soil  the  fingers  as 
bituminous  coal  does.  It  burns  with  a  short,  pale  blue  flame,  emits 
little  odor,  and  does  not  coke.  It  commonly  breaks  with  conchoidal 
fracture  and  thus  differs  from  bituminous  coal  which  usually  breaks 
into  roughly  rectangular  fragments  (Plate  IV,  Fig.  2).  When  very 
small  fractures  are  numerous,  the  freshly  broken  surface  shows 
small  rounded  or  oval,  eyelike  forms  and  it  has  then  been  called 
"Bird's-eye"  coal. 

The  calorific  value  of  anthracite  is  not  as  great  as  that  of  semi- 
bituminous  or  high  grade  bituminous  coal  because  it  does  not  develop 
a  high  temperature  so  rapidly.  This  is  owing  to  the  small  amount  of 
readily  combustible  material  compared  with  the  fixed  carbon.  It  is 

1  Analyses  of  coals  in  the  United  States.     Bur.  of  Mines,  Bull.  22,  1912. 

2  Trait6  de  mineralogie,  Tome  III,  p.  307,  1807. 

3  Op.  cit. 


ANTHRACITE  95 

much  sought  after  for  domestic  use  on  account  of  its  lack  of  soot  and 
dust  and  because  of  the  fact  that  it  burns  so  much  longer  than  other 
types  of  coal. 

Anthracite  reaches  the  maximum  hardness  in  coal.  It  varies  from 
2  to  2.5  in  Moh's  scale.  Certain  varieties  of  this  coal  are  capable 
of  being  cut  and  polished  for  ornamental  purposes  and  some  of  that 
from  the  Hazleton  and  Summit  Hill  districts  of  Pennsylvania  is 
used  for  this  purpose. 

Like  that  of  all  other  coals,  the  composition  of  anthracite  as  it  has 
been  mined  in  different  regions  varies  greatly.  The  following  figures 
show  the  variation  in  the  analyses  from  various  sources. 

Moisture o .  42-  5 . 61  per  cent 

Volatile  matter i .  72-10. 75        " 

Fixed  carbon 73 . 71-90 . 90       " 

Ash 3.20-30.09       " 

Sulphur o .  17-  2 . 60       " 

Hydrogen i .  89-  5.61       " 

Carbon 78.41-83.89       " 

Nitrogen 0.63-  i  .57       " 

Oxygen 3 . 80-11 . 54       " 

Calorific  value 9230-13,298  B.t.u. 

The  specific  gravity  varies  from  1.27  to  1.7. 

The  anthracite  from  Rhode  Island  is  not  included  in  the  above  list. 
There  the  coal  is  in  places  graphitic,  the  moisture  in  the  mine  sample 
runs  as  high  as  23  per  cent  and  the  fixed  carbon  as  low  as  49  per  cent 
because  of  very  high  ash,  although  the  volatile  matter  is  as  low  as 
2.5  per  cent.  The  ash  may  be  over  30  per  cent  and  the  oxygen  is 
high  except  in  the  dried  samples.  The  nitrogen  is  usually  below  0.5 
per  cent.  The  pecific  gravity  of  the  Rhode  Island  anthracite  varies 
from  1.43  to  2.21 

The  following  averages  represent  the  percentage  composition  of 
good  anthracite  calculated  on  a  moisture-free  and  ash-free  basis: 

Volatile  matter i .  50-  6 . 50  per  cent 

Fixed  carbon 93 . 00-98 .  oo       " 

Sulphur o. 50-  i . 50       " 

Hydrogen i .  75-  4 .  oo       " 

Carbon 90.00-94.00       " 

Nitrogen 0.60-  i .  25       " 

Oxygen 1.25-2.75       " 

Calorific  value 14,500-15,000  B.t.u. 

1  Ashley,  G.  H.,  Rhode  Island  coal.    U.  S.  Geol.  Survey,  Bull.  615,  1915 


96 


VARIETIES  AND   RANKS  OF  COAL 


The  moisture  will  run  from  2.5  to  4  per  cent  and  the  ash  from  1.5 
to  10  per  cent. 

The  specific  gravity  of  Pennsylvania  anthracite  varies  from  1.42 
to  i. 65,*  and  of  the  Welsh  anthracite  from  1.29  to  1.45,  averaging 
about  1.33. 

COMPARATIVE  COMPOSITION  OF  WOOD.  PEAT,  AND   COALS 

Table  showing  the  relative  percentage  composition  of  wood,  peat,  and  coals. 


Proximate  analyses 

Ultimate  analyses 

Calorific  value 

Kind  of  Fuel 

g 

| 

g 

g 

03 

5 

IS 

& 

rt 

^3 

0 

0 

0 

§ 

i  Cc/i 

,* 

d 

1 

rt  -jg 

O 

1 

3 

S 
"a 

CO 

I 

O 

| 

!• 

<5    o 

3 

« 

£ 

Wood  

6.25 

49.50 

.10 

43.15 

5,800 

Peat  a  

56.70 

26.14 

11.17 

5-99 

0.64 

8.33 

21.03 

.10 

62.91 

53.40 

1,992 

3,586 

Do  c  

60.37 

25.80 

13-83 

.48 

4.69 

48.57 

54 

28.89 

4,600 

8,280 

Lignite  a  

34-55 

35.34 

22.91 

7   20 

.10 

6.60 

42.40 

•  57 

42.13 

15.50 

3,939 

7,090 

Do  ft  

60.67 

39-33 

.89 

4  74 

72.79 

•98 

19.60 

6,762 

12,172 

Subbituminous  a  .  . 

24.28 

27.63 

44-84 

3  25 

.36 

6.14 

55-28 

.07 

33  90 

16.20 

5,209 

9,376 

Do  b 

38.12 

61.88 

4-  74 

76.28 

•  47 

17  01 

7,188 

_     o 

Bituminous  a  

3-24 

27.13 

62.52 

7-H 

•95 

5.24 

78.00 

23 

7.47 

i.  so 

7,733 

13,919 

Do  b  

30.26 

69.74 

.06 

S-39 

87.00 

•  37 

5.18 

8,626 

15,527 

Cannel  a 

I  70 

50.76 

9-31 

O2 

6.83 

73-25 

8.28 

o.  40 

14,251 

Do  b 

J.  .   /U 

42.96 

7.46 

82.31 

47 

7.61 

8,896 

16,013 

Semibituminous  a  . 

2.03 

14.47 

75-31 

8.19 

.26 

4.14 

79-97 

.26 

4.18 

1.40 

7,823 

14,081 

Dob  

16.12 

83.88 

•52 

4-37 

89.07 

-40 

2.64 

8,713 

15,683 

Semianthracite  a  .  . 

3.38 

8.47 

76.65 

11.50 

.63 

3.58 

78.43 

.00 

4.86 

2.60 

7,309 

13,156 

Dob  

9-95 

90-05 

•  74 

3.76 

92.15 

.18 

2.17 

8,587 

15.457 

Anthracite  a  

2.80 

1.16 

88.21 

7-83 

•89 

1.89 

84.36 

.'63 

4.40 

i  50 

7,388 

13,298 

Do  b  

1.29 

98.71 

.00 

1.77 

94-39 

.71 

2-13 

8,268 

14,882 

(a)  Sample  as  received. 

(b)  Same  sample  calculated  to  an  ash-  and  moisture-free  basis. 

(c)  Sample  calculated  to  a  moisture-free  basis. 

Peacock  coal.  —  Peacock  coal  is  not  a  distinct  variety  of  coal  but 
rather  a  condition  in  which  either  anthracite  or  bituminous  coal  may 
be  found.  It  is  of  considerable  interest  in  some  localities  because  of 
its  beauty  and  abundance.  It  has  received  its  name  from  its  irides- 
cent colors  which  resemble  those  o  the  peacock  in  their  changing 
lights.  This  play  of  colors  is  similar  to  that  produced  by  a  film  of 
oil  or  of  iron  oxide  on  water  and  is  due  to  the  same  cause,  viz.,  re- 
fraction and  interference  of  the  rays  of  light  in  passing  through  the 
film.  This  coal  is  found  only  in  the  upper  levels  of  the  mine,  par- 
1  Stock,  22d  Ann.  Kept.,  U.  S.  Geol.  Survey,  p.  74,  1900-1901. 


JET  97 

ticularly  where  the  seam  and  roof  slate  are  much  fractured,  thus  per- 
mitting surface  waters  to  percolate  through  the  fissures  in  the  coal 
and  to  deposit  thin  films  of  iron  oxide  along  the  cracks.  The  film  may 
in  a  few  cases  be  due  to  traces  of  crude  oil  or  to  sulphur  dioxide  but 
the  main  cause  is  the  iron  oxide  produced  by  the  oxidation  of  iron 
pyrite  near  the  surface  where  the  oxygen  of  the  air  can  attack  the 
iron  sulphide.  That  it  might  be  due  in  some  rare  cases  to  sulphur 
dioxide  gas,  which  may  be  set  free  in  the  weathering  of  iron  sulphide, 
is  suggested  by  the  fact  that  a  burning  sulphur  match  brought  close 
to  a  fragment  of  coal  will  often  produce  a  similar  iridescent  film  on  the 
surface  of  the  coal. 

Other  Combustible  Substances  Entering  Into  the  Composition 
of  Some  Coal  Seams 

Jet  (Fr.  Jayet,  Ger.  Gagath,  Greek,  Gagates).  —  This  is  a  black, 
rather  fibrous  to  compact  substance  capable  of  taking  a  good  polish 
and  used  in  Europe  for  the  manufacture  of  ornaments,  especially 
for  those  worn  in  mourning.  Formerly  an  industry  on  a  small  scale 
was  carried  on  in  France  at  Sainte-Colombe  sur  THero,  Departement 
de  PAude.  In  Yorkshire,  England,  a  few  tons  of  this  material  have 
been  produced  and  it  is  said  to  have  been  worth  about  a  shilling  a 
pound.  The  composition  of  jet  is  as  follows:1 

Volatile  matter 37 . 90  per  cent 

Ash 1.70       " 

Carbon 61 .40       " 

Its  specific  gravity  varies  from  1.26  to  1.3. 

Jet  is  generally  described  as  a  variety  of  lignite  but  Prestwich2 
speaks  of  it  as  a  wood  converted  into  a  sort  of  cannel  coal.  While 
jet  may  resemble  cannel  a  little  in  physical  character,  from  our  present 
knowledge  of  cannel  it  is  evident  that  it  cannot  resemble  it  in  origin 
since  all  writers  agree  that  jet  is  altered  wood  while  cannel  is  made 
up  almost  entirely  of  plant  spores.  The  jet  found  in  the  Jurassic 
rocks  on  the  Yorkshire  coast  of  England  is  believed  from  structure 
detected  in  thin  sections  to  have  been  formed  mainly  from  coniferous 
wood  which  was  allied  to  the  Araucarian  pines.  It  is  also  considered 
that  the  trees  drifted  to  their  present  position  since  the  jet  is  now 

1  Descloizeaux,  A.,  Manuel  de  mineralogie,  Tome  2,  p.  332,  1893. 

2  Prestwich,  J.,  Chemical,  physical,  stratigraphic  geology,  p.  142. 


98 


VARIETIES  AND   RANKS   OF   COAL 


found  associated  with  Ammonites  and  other  marine  fossils.  It  oc- 
curs in  Asia  Minor,  Spain  and  Bohemia  as  well  as  in  England  and 
France. 

Natural  coke  or  carbonite.  —  In  certain  cases  where  igneous  rocks 
have  intruded  bituminous  coal  seams  the  coal  has  been  transformed 
m  -  into  natural  coke  more  or  less 

resembling  artificial  coke  but 
usually  differing  from  the  latter 
chiefly  in  the  percentage  of  the 
volatile  constituents  which  it 
contains  and  in  its  more  com- 
pact character.  Taff1  has  sug- 
gested that  the  greater  percentage 
of  volatile  constituents  in  the 
natural  coke  may  be  due  to  the 
lack  of  opportunity  for  the  es- 
cape of  these  gases  and  to  the 
possible  accession  of  gases  to  the 
coke  from  the  adjacent  coal  seam 
after  it  has  cooled.  The  coke 
shows  a  typical  columnar  struc- 
ture varying  in  degree  of  perfec- 
tion of  the  columns  (Fig.  16), 
and  with  the  columns  normal  to 
the  surface  of  contact  between 
the  igneous  rock  and  the  coal 
which  has  been  coked.  The  ex- 
tent to  which  the  coal  is  coked 


FIG.  16.  —  Natural  coke,  or  carbonite 

from  Hesse  (specimen  in  collection  of 

Museum  Nationale  d'Histoire  Naturelle, 

Paris). 


varies  greatly.  Other  things 
being  equal,  there  will  be  a  fairly 
close  relation  between  the  thick- 
ness of  the  coked  zone  and  that 
of  the  igneous  rock,  the  former  varying  directly  as  the  latter,  but 
no  definite  rule  can  be  established  because  cases  have  been  noted 
where  almost  no  observable  coking  has  occurred,  while  in  other  cases 
the  coal  is  coked  out  of  all  proportion  to  the  size  of  the  intruding 
rock.  This  condition  is  well  understood  when  one  considers  that 

i  Taff,  J.  A.,  Natural  coke  in  the  Wasatch  Plateau.     Science,  N.  S.,  Vol.  23,  p.  696, 1906. 


NATURAL  COKE  OR  CARBONITE  99 

igneous  masses  entering  the  coal  seams  at  various  times  or  in  differ- 
ent places  may  vary  greatly  in  temperature  and  in  the  amount  of 
the  hot  vapors  and  gases  which  they  carry.  In  some  cases  the 
latter  may  escape  along  the  bedding  planes  in  the  coal  deposits 
and  conduct  the  heat  some  distance  from  the  igneous  rock.  The 
basic  igneous  rocks,  being  more  fluid  than  the  acid  are  often  capa- 
ble of  intruding  themselves  into  narrow  fissures  in  ways  in  which 
the  more  viscous  acid  rocks  cannot. 

In  the  United  States  natural  coke  is  common  in  Colorado,  Utah, 
and  New  Mexico,  and  it  is  also  abundant  in  Mexico1  and  Alaska  where 
the  coals  have  been  extensively  intruded  by  igneous  rocks. 

This  coke  has  a  regular  fracture,  is  dark  gray  to  iron-black  in  color, 
and  its  texture  varies  from  distinctly  porous  to  compact.  The  luster 
is  graphitic  to  submetallic.  It  often  grades  into  anthracite  which  in 
turn  passes  into  the  bituminous  coal  of  the  seam.  In  most  places  it 
makes  excellent  fuel.  The  following  analyses  indicate  the  per- 
centage composition  of  the  coke,  the  adjacent  coal,  and  a  sample  of 
artificial  coke. 

I       II  III      IV      V      VI       VII  VIII*    ix*     x* 

Moisture 8.10    0.32  0.57    3.86  13.42    3.28    0.184 

Volatile  matter  40.20  20.38  0.39  35.34     5.83     1.64    0.552  20.30  12.20    4.70 

Fixed  carbon     .45.91  65.90  78.24  53.28  61.50  89.14  88.726  79.70  87.80  95.30 


Ash 

Sulphur.  . 
Hydrogen 
Carbon.  . 


5.76  13.10  20.80     7.52  19.25     9.22     9.993     8.29    9.73  45.96 
0.54    0.64     0.48     0.83     0.533     2.07     i. ii     0.15 

5-48     3-39 
72.66  61.55 


Nitrogen 1.17     0.81 

Oxygen  12.53  14.52 

Air-drying  loss  .  2 . 60  1 1 . 60 

B.t.u 13,068  9895 

I.   Analysis  quoted  by  Taff  of  coal  in  seam  in  Wasatch  Plateau. 
II.   Natural  coke  from  same  seam. 

III.  Natural  coke  from  Cokedale  Mine,  Colorado.     U.  S.  Bur.  of  Mines,  Bull.  22,  pt.  i, 

p.  69. 

IV.  Coal  taken  i  foot  from  natural  coke  and  z\  feet  from  a  dike.     Walsen  Mine, 

Colorado.     Op.  cit.  under  III,  p.  65. 
V.   Same  locality  as  IV  but  close  to  small  dike  and  coke. 
VI.  Artificial  coke. 

VII.   Artificial  coke  from  the  coal  of  the  Connelsville  basin,  Pa.      U.  S.  Geol.  Survey. 
VIII.    Coal  in  the  seam  removed  from  the  influence  of  the  eruptive. 
IX.    Coal  0.3  metres  from  the  igneous  rock. 
X.   Coal  in  contact  with  the  eruptive. 

*  Analyses  by  G.  von  Rath.  Contactverhaltnisse  Zwischen  Kohle  und  einem  basischen 
Eruptivgestein  bei  Fiinf kirchen :  Neues  Jahrbuch,  I,  pp.  274-277,  1880. 

1  Durable,  E.  T.,  Natural  coke  of  the  Santa  Clara  Coal-Field,  Sonora,  Mexico.  Trans. 
Am.  Inst.  Min.  Eng.,  Vol.  29,  pp.  546-549,  1899. 


100  VARIETIES  AND   RANKS  OF  COAL 

The  greater  percentage  of  ash  shown  in  the  analyses  of  the  coke 
than  in  the  analyses  of  the  coal  from  the  same  seam  is  often  only  rela- 
tive, but  in  some  cases  it  is  probable  that  silica  and  possibly  other 
mineral  constituents  have  been  added  to  the  seam  by  the  igneous 
rock  in  its  immediate  vicinity. 


FIG.  17-  —  Intrusion  of  diabase  into  a  coal  seam  in  Alaska,  producing 
natural  coke.     (From  a  sketch  by  W.  R.  Crane.) 

Mineral  charcoal  or  "mother  of  coal"  (Fr.  Fusain). —  In  the 
different  varieties  of  coal  from  lignite  to  anthracite  there  are  dull 
laminae,  lenses,  and  irregular  bands  of  a  black  to  dark-grey  material 
which,  on  account  of  its  resemblance  to  charcoal  is  known  as 
" mineral  charcoal"  or  among  many  of  the  miners  as  " mother  of 
coal."  It  may  take  the  form  of  an  iron-gray,  almost  powdery 
material  or  it  may  show  the  outline  of  blackened  fragments  still 
retaining  some  of  the  original  woody  structure  and  fibers.  In 
some  cases  even  the  most  delicate  structures  of  the  leaf  are  pre- 
served. When  cut  with  a  knife  it  shows  much  the  same  consistency 


MINERAL   CHARCOAL   OR     MOTHER   OF   COAL"  101 

as  wood  charcoal  but  is  more  sooty  and  crumbling.  It  soils 
the  fingers.  Various  explanations  have  been  offered  for  its  origin. 
Daubree1  in  1844  ascribed  it  to  forest  fires  started  by  lightning,  burn- 
ing in  the  swamps  where  the  coal  vegetation  was  laid  down.  As  early 
as  1858  Rogers2  recognized  that  it  was  due  to  some  alteration  which 
the  vegetation  suffered  before  being  buried  and  this  explanation  is 
supported  by  White,3  who  considers  that  the  association  of  the  various 
woody  materials,  the  preservation  of  the  rods,  and  the  delicate 'fern- 
leaf  fragments  make  the  forest  fire  hypothesis  untenable.  He  be- 
lieves that  the  charcoal  has  originated  as  a  result  of  the  greater  amount 
of  decomposition  which  the  vegetation  suffered  before  being  buried  in 
the  bog.  On  the  other  hand,  Jeffrey4  still  clings  to  the  theory  that 
the  forest  fire  was  the  agent  which  produced  the  charcoal. 

A  consideration  of  the  actions  of  forest  fires  in  our  modern  swamps 
and  peat-bogs  in  the  northern  portions  of  the  continent,  in  addition 
to  the  arguments  put  forth  by  White,  oppose  the  forest  fire  hypothesis. 
It  is  seldom  that  the  fire  leaves  the  charred  materials  in  such  quan- 
tities in  proportion  to  the  ash  and  in  such  associations  in  relation  to 
the  coarse  and  fine  fragments  as  that  in  which  they  must  generally 
have  been  left  to  produce  the  deposits  now  found  in  coal.  It  is 
possible  that  an  occasional  mass  of  charcoal  resulted  from  fire  but 
improbable  that  the  greater  part  of  the  mineral  charcoal  was  produced 
in  that  way.  The  best  explanation  is  found  in  the  greater  alteration 
of  the  vegetal  matter  in  parts  of  the  swamp  exposed  to  dry  rot  where 
the  water  was  low. 

It  is  evident  that  carbonite  and  mineral  charcoal  have  at  times 
been  confused  by  some  writers.5 

Analyses  show  that  mineral  charcoal  usually  differs  considerably 
in  chemical  composition  from  the  other  portions  of  the  coal  seam 
in  which  it  occurs.  The  following  analyses  were  made  from  a  seam 
in  which  the  charcoal  occurs  irregularly  throughout  the  mine  and  is 
there  known  as  " mother  of  coal."  It  is  not  found  over  9  inches  from 
the  bottom  of  the  seam  and  it  always  pinches  out  gradually.  The 

1  Daubree,  A.,  Compt.  Rend.,  Vol.  19,  p.  126,  1844. 

2  Rogers,  H.  D.,  Geology  of  Pennsylvania,  Vol.  2,  p.  993,  1858. 

3  White  and  Thiessen,  The  origin  of  coal.     U.  S.  Bur.  of  Mines,  Bull.  38,  p.  33,  1913. 

4  Jeffrey,  E.  C.,  Jour,  of  Geology,  Vol.  23,  p.  218,  1915. 

6  Heinrich,  O.  J.,  The  Mesozoic  formation  in  Virginia.  Trans.  Am.  Inst.  of  Min. 
Eng.,  Vol.  6,  pp.  243-244,  1877-78. 


102  VARIETIES   AND   RANKS  OF   COAL 

thickness  of  the  charcoal  varies  from  zero  to  3  inches.  There  are 
usually  very  small  bright  streaks  running  through  the  dark  gray, 
which  always  has  a  dull  luster.  The  writer  is  indebted  to  Mr.  H.  B. 
Northrup  for  these  analyses. 

I  II 

Moisture o .  62  per  cent   o .  23  per  cent 

Volatile  matter 23 . 05        "         7.11        " 

Fixed  carbon 68.86        "       90.99        " 

Ash 7.47        "         1.67        " 

Sulphur 1.19        "         o .  23        " 

I.   The  coal  from  a  seam  in  the  Glenview  Mine,  Decatur  Twp.,  Clearfield  Co.,  Pa. 
II.   Mineral  charcoal  from  the  same  seam. 

Resinous  substances.  —  In  addition  to  the  substances  described 
there  are  often  found  in  coals,  particularly  in  the  younger  and  less 
altered  coals  such  as  the  lignites,  large  and  small  masses  of  amber- 
like substances  which  represent  the  resins  from  various  trees  growing 
in  the  coal  swamps.1  To  these  the  name  Retinite  is  often  applied  in  a 
general  way.  In  the  Tertiary  lignites  near  Gore,  New  Zealand, 
masses  of  this  retinite  as  large  as  a  man's  head  may  be  seen  and 
in  some  of  the  lignite  of  the  western  United  States  resins  are  found 
in  considerable  quantities.  The  following  are  examples  of  these 
resins  from  coal  seams  in  various  localities.2 

Ambrite  (C4oH66O5  approx.):  A  yellowish-gray,  subtransparent, 
amorphous  resin  which  breaks  with  a  conchoidal  fracture.  The 
hardness  is  2  and  the  specific  gravity  1.034.  The  luster  is  greasy. 
It  becomes  strongly  electrified  when  subjected  to  friction.  An  an- 
alysis by  Maly  shows: 

Ash o.  19  per  cent 

Hydrogen 10 . 58 

Carbon 76.53 

Oxygen 12 . 70       " 

It  burns  with  a  yellow  smoky  flame.     It  is  insoluble  in  ether,  oil  of 
turpentine,  benzine,  chloroform,  and  dilute  acid. 

This  resin  is  described  by  Hochstetter  as  occurring  in  large  masses 
in  several  of  the  coal  fields  of  New  Zealand.  It  is  so  much  like  the 
Kauri  gum  of  the  North  Island  that  it  is  sometimes  exported  with  it. 

1  White,  David,  Resins  in  Paleozoic  plants  and  in  coals  of  high  rank.     U.  S.  Geol. 
Survey,  Prof.  Paper  85  E,  1914. 

2  For  full  description  of  these  and  related  substances  see  Dana's  System  of  mineralogy, 
pp.  1002-1014,  1892.    Also,  Descloizeaux,  Manuel  de  mineralogie,  Tome  2,  p.  34,  1893. 


RESINOUS  SUBSTANCES  103 

Bathmllite:  This  substance  forms  dull  brown  lumps  in  the  Tor- 
banite  in  Scotland  and  since  it  usually  occurs  as  a  cavity  filling  it  is 
not  known  whether  it  is  a  resin  or  a  secretion  from  the  Torbanite 
which  it  resembles  in  composition  although  containing  less  oxygen. 

Duxite:  A  dark  brown,  opaque  resin  from  the  lignite  at  Dux, 
Bohemia.  Its  specific  gravity  is  given  as  1.13  and  its  chemical  com- 
position according  to  Fischer  is  as  follows : 

Moisture 2.72  per  cent 

Ash 1.94       " 

Sulphur o .  42       " 

Hydrogen 8 . 14       " 

Carbon 78 . 25       " 

Oxygen 13-19       " 

This  is  in  general  similar  to  Muckite  and  Walchowite  except  that 
they  are  lighter  colored.  Neudorfite  from  the  coal  beds  at  Neudorf, 
Moravia  is  very  similar  in  composition. 

Middletonite:  This  substance,  which  was  named  by  Johnston1 
from  the  Middleton  Collieries  near  Leeds,  England,  occurs  about  the 
middle  of  the  main  coal  in  little  round  masses.  These  masses  are 
seldom  larger  than  a  pea  and  are  generally  in  thin  layers  less  than  T\ 
inch  in  thickness  between  the  layers  of  coal.  It  is  hard  and  brittle, 
and  its  specific  gravity  is  about  1.6.  In  color  it  is  reddish-brown  in 
reflected  light  and  deep  red  in  transmitted  light.  The  luster  is  resin- 
ous. It  blackens  on  exposure  to  the  air  and  then  cannot  readily  be 
distinguished  from  the  coal  except  by  its  luster.  It  is  unaffected  by 
heat  at  400°  F.  and  it  burns  like  resin.  It  is  soluble  in  cold  sulphuric 
acid  but  it  is  very  slightly  soluble  in  alcohol,  ether  and  oil  of  turpentine. 
An  analysis  shows  the  following  composition: 

Hydrogen 8 . 007  per  cent 

Carbon 86.437 

Oxygen 5 . 563       " 

The  formula  suggested  is  (C2oHi0  +  H2O)  which  resembles  that  for 
the  hydrate  of  the  oil  of  turpentine. 

Succinite:  This  substance  is  commonly  known  as  amber.  It  is 
found  in  considerable  quantities  on  the  coast  of  the  Baltic.  It  occurs 
as  irregular  masses  which  have  a  conchoidal  fracture.  The  hardness 
is  about  the  same  as  that  of  anthracite  coal,  2-2.5,  and  the  specific 
gravity  is  1.05  to  1.09.  The  color  is  yellow  or  reddish-brown  and  the 
luster  resinous.  It  is  negatively  electrified  by  friction  and  it  softens 

1  Johnston,  F.  W.,  The  Phil.  Mag.,  Vol.  12,  p.  261,  1838. 


104  VARIETIES  AND   RANKS  OF  COAL 

at  150°  C.  Its  composition  is  represented  by  the  following  analysis 
by  Schrotter: 

Hydrogen 10.22  per  cent 

Carbon 78.82       " 

Oxygen 10 . 94       " 

There  is  usually  a  little  sulphur  present  in  the  form  of  an  organic 
compound.  Succinite  occurs  in  the  bituminous  coals  of  the  southern 
part  of  France  and  in  lignite  in  various  localities. 

Wheelerite:  In  the  Cretaceous  lignite  beds  of  New  Mexico  Loew1 
found  a  yellowish  resin  filling  fissures  and  interstratified  with  the 
coal.  This  was  named  Wheelerite  after  Lt.  G.  M.  Wheeler.  The 
composition  is  as  follows: 

Hydrogen 7.31  per  cent 

Carbon 73 .  n        " 

Oxygen 19 . 58       " 

It  is  almost  entirely  dissolved  in  alcohol  or  ether  and  is  partially 
soluble  in  carbon  bisulphide.  It  is  soluble  also  in  sulphuric  acid, 
producing  a  brown  solution,  and  with  nitric  acid  it  evolves  nitrous 
fumes.  It  melts  at  154°  C. 

There  are  numerous  other  resins  similar  in  many  respects  to  those 
described  above.  Among  these  might  be  mentioned  lonite  from  the 
lignite  of  lone  Valley,  California;  Koflach  from  the  Tertiary  brown 
coals  of  Styria;  Rosthornite,  the  brown  to  garnet-red  material  which 
forms  lenticular  masses  in  the  coal  of  Carusthia;  Schleretinite  from 
the  Coal  Measures  of  Wigan,  England;  Tasmanite  from  the  bituminous 
shales  of  Tasmania;  Trinkerite  which  forms  large  amorphous  masses 
of  a  hyacinth-red  to  chestnut-brown  color  in  the  brown  coal  near 
Albona,  Istria.  Pyroretinite  which  resembles  the  resin  of  Pinus 
abies  is  said  to  occur  in  masses  from  the  size  of  a  nut  to  that  of  a 
man's  head  in  the  brown  coal  near  Ausseg,  Bohemia.  Its  specific 
gravity  runs  from  1.05  to  1.18  and  its  hardness  about  2.5.  Rochled- 
erite  occurs  in  large  reddish-brown  resin-like  masses  in  the  brown  coal 
of  Zweifelsruth  in  Eger,  Bohemia. 

1  Loew,  O.,  On  wheelerite,  a  new  fossil  resin.  Am.  Jour.  Sci.  $d  Series,  Vol.  7,  p.  571, 
1874. 


CHAPTER  V 
THE   CLASSIFICATION   OF   COALS 

Introduction 

There  have  been  in  use  since  the  earliest  days  of  the  coal  trade 
certain  names  which  distinguish  different  varieties  of  coal,  such  as 
anthracite,  bituminous,  and  lignite.  These  names,  or  their  equiva- 
lents, are  in  general  use  almost  throughout  the  world.  As  the  im- 
portance of  the  coal  trade  increased,  however,  it  was  realized  that  some 
more  definite  means  of  classifying  coals  according  to  their  composition 
and  heating  value  was  desired  because  the  lines  of  distinction  between 
the  varieties  used  in  the  past  were  not  sufficiently  definite  for  prac- 
tical purposes. 

Frazer's  Classification 

One  of  the  first  in  this  country  to  attempt  a  definite  classification  of 
coals  on  the  basis  of  their  composition  and  heating  value  was  Persifor 
Frazer,  Jr.1  He  based  his  classification  on  the  ratio  of  the  fixed  car- 
bon to  the  volatile  combustible  matter  (C  :  V.Hc).  He  states  that 
as  early  as  1844  W.  R.  Johnson  had  used  the  same  principle  and  had 
recognized  the  ratio  of  the  volatile  to  fixed  combustible  matter  as  a 
logical  basis  for  the  classification  of  coals.  After  various  attempts  to 
make  the  fuel  ratio  of  the  different  coals  fit  the  descriptions  of  the 
varieties  suggested  by  H.  D.  Rogers  in  1858,  Frazer  concluded 
that  it  is  only  possible  to  classify  the  coals  according  to  their  fuel  ratio 
within  wide  limits,  and  suggests  the  following  divisions: 

C 
V.Hc 

Hard-dry  anthracite 100-12 

Semianthracite 12-8 

Semibituminous 8-5 

Bituminous 5-0 

The  table  is  deficient  for  modern  use  because  it  does  not  distinguish 

1  Frazer,  Persifor,  Jr.,  Classification  of  coals.  Second  Geol.  Survey  of  Pennsylvania, 
Kept.  M.  M.,  pp.  128-144,  1879.  Also  Trans.  Am.  Inst.  Min.  Eng.,  Vol.  6,  pp.  430-451, 
1877,  and  Vol.  36,  p.  825,  1906 

105 


106  THE   CLASSIFICATION  OF   COALS 

subbituminous  coal  and  lignite  from  bituminous  coal  and  as  stated 
by  Frazer  the  ratio  limits  had  to  be  arbitrarily  chosen.  The  table 
represents,  however,  a  considerable  advance  over  any  previous  work 
and  it  sets  forth  a  principle  which  has  become  deeply  established  in 
the  coal  trade. 

In  discussing  Frazer's  classification,  A.  S.  McCreeth1  calls  attention 
to  the  fact  that  the  sulphur  content  of  the  coal  should  be  taken  into 
consideration  since  it  is  partly  volatilized  in  coking,  and  he  suggests 
that  the  portion  volatilized  should  be  subtracted  from  the  volatile 
hydrocarbon  percentage  and  added  to  that  of  the  fixed  carbon. 

Classification  on  basis  of  Moisture  Content 

In  1903  Collier2  suggested  that  all  coals  with  a  moisture  content  of 
10  per  cent  or  more  should  be  classed  as  lignite,  and  those  with  less 
than  10  per  cent  as  bituminous,  but  his  classification  has  proved  en- 
tirely unsatisfactory. 

Campbell's  Classification 

After  extensive  studies  of  coal  for  the  purpose  of  obtaining  a  satis- 
factory classification  Campbell3  came  to  the  following  conclusions: 
(i)  For  the  higher  grades  of  coal  the  fuel  ratio  may  be  used  as  a  satis- 
factory means  of  separation  but  it  does  not  properly  separate  the 
lignites  and  bituminous  coals.  (2)  The  percentage  of  fixed  carbon 
cannot  be  used  as  a  satisfactory  basis.  (3)  The  calorific  value  cannot 
be  used  since  many  of  the  bituminous  coals  are  of  higher  calorific 
value  than  the  best  grades  of  anthracite.  It  is,  however,  fairly  satis- 
factory for  the  lignites  and  bituminous  coals.  (4)  The  percentage  of 
hydrogen  present  is  valueless  as  a  basis  of  classification.  (5)  A  classi- 
fication according  to  the  carbon  content  is  satisfactory  in  a  general 
way  as  there  is  a  fairly  regular  decrease  in  the  carbon  content  from  that 
of  anthracite  to  that  of  lignite.  The  separation  between  anthracite 
and  semibituminous  is  not  marked  and  there  are  many  exceptions 
to  the  rule.  (6)  The  carbon-hydrogen  ratio  is  regarded  as  the  most 
satisfactory  basis  for  classification. 

1  McCreeth,  A.  S.,  Second  Geol.  Survey  of  Pennsylvania,  Rept.  M.  M.,  p.  157,  1879. 

2  Collier,  A.  J.,  Coal  resources  of  the  Yukon,  Alaska;   U.  S.  Geol.  Survey,  Bull.  218, 
1003. 

3  Campbell,  M.  R.,  The  classification  of  coals.     Am.  Inst.  of  Min.  Eng.,  Vol.  36,  p.  324, 
1906.     Also,  Report  on  the  operation  of  the  coal  testing  plant.     U.  S.  Geol.  Survey, 
Prof.  Paper  48,  pt.  i,  1906. 


SEYLER'S   CARBON-HYDROGEN   CLASSIFICATION 


107 


He  then  groups  the  coals  as  follows  in  a  tentative  classification, 
the  ratios  of  the  higher  coals  being  rather  indefinite  owing  to  lack  of 
ultimate  anlyses. 

Carbon-Hydrogen  Ratio. 

Group  A      (Graphite) oo-(?) 

Grouo  B 
Group  C 
Group  D 
Group  E 
Group  F 
Group  G 
Group  H 
Group  I 
Group  J 
Group  K 
Group  L 


(Semianthracite) 26(?)-23(?) 

(Semibituminous) 23(?)-2o 

20-17 

(Bituminous) I4'™ 

I2.5-II.2 

(Lignite) 11.2-  9.3 

(Peat) 9-3-  (?) 

(Wood,  Cellulose) 7.2 


Seyler' s  Carbon-Hydrogen  Classification 

Seyler1  had  previously  published  the  following  classification.  It  is 
based  on  the  hydrogen  and  carbon  in  the  pure  coal.  The  genera, 
which  are  arranged  vertically,  are  distinguished  by  their  hydrogen 
content  while  the  species  are  arranged  horizontally  and  separated 
according  to  their  percentage  of  carbon.  This  table  is  taken  from 
Pollard.2 

1  Seyler,  C.  A.,  Chemical  classification  of  coal.     Proc.  S.  Wales  Inst.  Eng.,  Vol.  21, 
p.  483  and  Vol.  22,  p.  112.     Also,  Colliery  Guardian  LXXX  pp.  17-19,  80-82  and  134-136. 

2  Strahan,  A.,  and  Pollard,  W.,  The  coals  of  S.  Wales.    Mem.  Geol.  Survey  of  England 
and  Wales,  2d  ed.,  pp.  58-59,  1915. 


io8 


THE   CLASSIFICATION  OF   COALS 


Carbon 

Anthracitic 

Carbon- 
aceous 

Bituminous 

Lignitious 

Meta. 

Ortho. 

Para. 

Meta.    Ortho. 

Carbon 
over  93  .  3 

93-3-91.2 

91.2-89.0 

89.0-87.0 

87.0-84.0 

84-80       80-75 

Perbitu- 
minous 
genus 

Hydrogen 
over  5.  8 
per  cent 

Perbitu- 
minous 
(Per-meta- 
bitumi- 
nous) 

Perbitu- 
minous 
(Per-ortho- 
bitumi- 
nous) 

Perbitu- 
minous 
(Per-para- 
bitumi- 
nous) 

Perligni- 
tious 

Bitumi- 
nous 
genus 
Hydrogen 
5-0-5-8 
per  cent 

Pseudobi- 
tumi- 
nous 
species 

Metabitu- 
minous 

Orthobitu- 
minous 

Parabitu- 
minous 

Lignitious 
(Meta) 
(Ortho) 

Semibitu- 
minous 
genus 

Hydrogen 

4-5-5-0 
per  cent 

Semibitu- 
minous 
species 

(Ortho- 
semibi- 
turni- 
nous) 

Subbitu- 
minous 
(Sub-meta- 
bitumi- 
nous) 

Subbitu- 
minous 
(Sub-or- 
thobitu- 
minous) 

Subbitu- 
minous 
(Sub-para- 
bitumi- 
nous) 

Subligni- 
tious 
(Meta) 
(Ortho) 

Carbon- 
aceous 

genus 

Hydrogen 
4.0-4.5 
per  cent 

Semian- 
thracitic 

species 

Carbon- 
aceous 

species 

(Ortho- 
carbon- 
aceous) 

Pseudo- 
carbon- 
aceous 
(Sub- 
metabi- 
tumi- 
nous) 

Pseudo- 
carbon- 
aceous 
(Sub-or- 
thobitu- 
minous) 

Pseudo- 
carbon- 
aceous 
(Sub-para- 
bitumi- 
nous) 

Anthra- 
citic 
genus 
Hydrogen 
under  4 
per  cent 

Orthoan- 
thracitic 

Pseudoan- 
thracite 

Subcar- 
bon- 
aceous 

Pseudoan- 
thracite 

Sub-meta- 
bitumi- 
nous 

Pseudoan- 
thracite 

Sub-ortho- 
bitumi- 
nous 

Pseudoan- 
thracite 

Sub-para- 
bitumi- 
nous 

Pollard  shows  that  in  the  coals  analysed  from  the  Welsh  field  the 
hydrogen-carbon  ratio  falls  fairly  satisfactorily  into  Seyler's  classi- 
fication. The  carbon-hydrogen  ratios  given  by  the  U.  S.  Geological 
Survey  do  not  fit  the  Welsh  anthracites  very  well  as  many  of  them 
have  a  ratio  below  26. 


PARR'S   CLASSIFICATION 


109 


Grout's  Classification  based  on  Carbon  Content 

In  an  article  published  the  year  after  Campbell's  classification 
appeared,  Grout1  criticizes  the  use  of  the  carbon-hydrogen  ratio  as 
not  being  reliable  and  states  that  if  total  carbon  in  ash-  and  moisture- 
free  coal  had  been  considered  the  separation  between  lignite  and 
bituminous    coal   would   have   been   very    satisfactory.     The    chief 
objection  made  to  the  carbon-hydrogen  ratio  is  the  fact  that  although 
the  hydrogen  content  of  lignite  and  bituminous  coal  is  not  so  very 
different,  the  variation  may  amount  to  one-third  of  the  total  and  thus 
give  a  large  difference  in  ratio  in  coals  which  are  not  markedly  differ- 
ent in  other  respects;    on  the  other  hand,  it  may  throw  two  coals 
together  which  are  unlike  in  many  important  respects.     The  diffi- 
culty in  sampling  the  low  grade  coals  so  that  all  collectors  may  be 
able  to  get  the  same  amount  of  moisture  and  therefore  the  same 
amount  of  hydrogen  in  the  coal  from  the  same  seam  is  a  further  ob- 
jection to  Campbell's  carbon-hydrogen  ratio  since  it  is  based  on  too 
variable  a  factor. 

The  following  is  Grout's  classification  based  on  fixed  carbon  for 
those  coals  above  bituminous,  and  on  fixed  carbon  and  total  carbon 
for  bituminous  coals  and  those  of  lower  grade. 

Graphite  ...............................     Fixed  carbon  over  99  per  cent 

Anthracite  ..............................     Fixed  carbon  over  93        " 

Semianthracite  ..........................     Fixed  carbon  83-93          " 

Semibituminous  .........................     Fixed  carbon  73-83          " 

Bituminous: 

grade  ........................... 


Cannel  /  Fixed  carbon  35~48 

.......   I  Total  carbon  76.2- 


76.2-88 


Peat  and  turf  /  Fixed  carbon  below  55 

Peat  and  turf  ...........................  (Total  carbon  bdow 


Wood 


Parr's  Classification 

Parr,2  in  his  classification,  considers  that  the  term  volatile  combus- 
tible as  it  has  generally  been  used  is  incorrect  since  it  includes  some 

1  Grout,  F.  F.,  The  composition  of  coals.     Econ.  Geology,  Vol.  2,  pp.  225-241,  1907. 

2  Parr,  S.  W.,  Illinois  Geol.  Survey,  Bull.  3,  1906.     Also,  The  classification  of  coals. 
Jour.  Am.  Chem.  Soc.,  Vol.  28,  p.  1425,  1906. 


no 


THE    CLASSIFICATION  OF   COALS 


hydrogen,  oxygen,  and  nitrogen,  which  are  non-combustible.  The 
hydrogen  present  as  hydrocarbons  is  combustible  but  that  combined 
with  oxygen  in  water  is  not.  For  example,  in  a  Pocahontas  coal  with 
18.7  per  cent  volatile  matter  14.5  per  cent  is  combustible  hydrocarbons 
and  4.2  per  cent  is  non-combustible  hydrogen,  oxygen  and  nitrogen. 
This  inert  matter  should  be  taken  into  consideration  since  it  is  not 
an  asset  to  the  fuel. 

In  this  classification  total  carbon  (C)  and  fixed  carbon  (fc)  are 
determined  from  analysis.  The  volatile  carbon  (vc)  unassociated 
with  hydrogen  is  obtained  by  subtracting  the  percentage  of  fixed 
carbon  from  that  of  total  carbon  (C  —  fc  =  vc).  The  inert  volatile 
matter  is  obtained  by  subtracting  from  100  per  cent  the  sum  of  total 
carbon  +  sulphur  -f  ash  +  water  -f  hydrogen,  which  is  not  united 
with  oxygen  in  water  and  is,  therefore,  free  to  burn  and  produce  heat. 
To  reduce  this  remainder  to  a  pure  fuel  basis  it  is  divided  by  100  less 
the  sum  of  ash  and  water.  The  derived  formula  on  which  the  fol- 


lowing  table  is  based  is  vc 


100 


This  ratio  serves  to  differentiate 


the  coals  above  bituminous.  In  the  bituminous  and  lower  grades  of 
coal  the  inert  volatile  matter,  which  is  so  much  more  abundant  in 
these  coals,  is  taken  into  consideration.  The  classification  is  as 
follows : 


IOO 

vc  — 

Inert  volatile 

C 

Anthracites  proper  . 

.  .  .  Below  4 

Anthracitic  \ 

Semianthracites  .  .  . 

.  .  .       4-8 

. 

Semibiturninous 

10—  i^ 

A  20-32 

5-io 

Bituminous 

Bituminous  proper 

B  20-27 
C  32-44 
D  27-44 

10-15 
5-io 
10-15 

Black  lignite  
Brown  lignite 

27  up 
27  up 

16-20 
20—30 

In  taking  examples  of  the  various  analyses  of  coals  tested  by  the 
U.  S.  Geological  Survey  at  the  St.  Louis  plant,  Parr1  shows  that  they 
readily  follow  this  classification. 

1  U.  S.  Geol.  Survey,  Prof.  Paper  48,  1906. 


WHITE'S   CLASSIFICATION   BASED   ON   CARBON  in 

A  further  formula  is  suggested  for  the  purpose  of  determining  what 
Parr  chooses  to  call  the  "  gross  coal  index,"  or  the  amount  of  any  coal 
necessary  to  give  100  pounds  of  pure  fuel.  It  is  found  by  adding 
together  the  carbon,  sulphur  ,and  combustible  hydrogen,  (these  three 
constituents  being  regarded  as  the  only  true  heat-producing  factors 
in  the  coal)  dividing  the  sum  by  100,  and  100  by  the  quotient.  Thus 
a  Dakota  lignite  contains:  C  52.66  per  cent;  H  1.83  per  cent;  and  5 
2. 02  per  cent  =  56.51.  The  " gross  coal  index"  for  this  coal  would 

be =  177,  or  it  would  require  177  pounds  of  it  to  make  100 

-5651 
pounds  of  pure  fuel. 

Grout's  classification  resembles  this  one  of  Parr's  in  providing  two 
factors  for  fixing  the  position  of,  the  coal  and  it  has  the  advantage  of 
being  simpler  in  its  application. 

White's  Classification  based  on  Carbon  —  Oxygen  +  Ash 

Content 

Another  method  of  classifying  coals  has  been  suggested  by  White1 
in  making  determinations  of  the  anti-calorific  influence  of  oxygen. 
As  a  result  of  an  investigation  of  all  available  ultimate  analyses  it 
was  found  that  ash  and  oxygen  possess  almost  equal  anti-calorific 
values,  the  former  having  slightly  more  than  the  latter.  This  was 
found  to  be  true  also  for  moisture-free  coal.  If  two  coals  alternate 
in  the  percentages  of  ash  and  oxygen  while  the  other  constituents 
remain  constant  the  calorific  value  changes  very  little.  Since  carbon 
is  the  principal  calorific  element  in  the  fuel  it  seems  appropriate  that 
it  should  be  taken  as  one  factor  and  (oxygen  -f  ash)  as  the  other  in 
determining  the  calorific  value.  It  is  found,  therefore,  that  the 
ratio  C  :  (O  +  ash)  gives  a  quotient  which  corresponds  very  closely 
to  the  determined  calorific  value  of  the  coal,  not  varying  more  than 
i  per  cent,  as  a  rule,  from  an  efficiency  curve.  The  sulphur,  available 

hydrogen  f  H  —  —  j  and  nitrogen  seem  to  play  a  small  part  in  con- 
trolling the  calorific  value  of  the  fuel  compared  with  that  of  the 
carbon,  oxygen,  and  ash.  The  hydrogen  is  the  most  potent  element 
of  the  three  and  its  influence  is  shown  in  the  special  types  of  coal 
such  as  those  of  the  boghead-cannel  group. 

1  White,  David,  The  effect  of  oxygen  in  coal.     U.  S.  Geol.  Survey,  Bull.  382,  1909. 


112  THE   CLASSIFICATION  OF   COALS 

It  was  found,  further,  that  the  relation  of  the  ratio  C  :  (O  +  ash) 
to  the  calorific  value  becomes  much  less  distinct  in  coals  undergoing 
anthracitization  and  having  over  79  per  cent  fixed  carbon  in  the  pure 
fuel,  or  in  those  which  have  been  weathered. 

This  classification  is  of  great  scientific  interest  in  its  bearing  on  the 
calorific  value  of  coals  but  it  has  little  application  in  classifying  coals 
according  to  the  terms  which  are  familiar  in  the  coal  trade. 

There  is  one  strong  objection,  from  a  practical  standpoint,  to  all 
the  preceding  classifications  except  that  of  Frazer  in  the  fact  that  they 
require  ultimate  anlyses.  If  possible,  the  making  of  ultimate  an- 
alyses for  classification  purposes  should  be  avoided  since  they  are 
always  costly.  Parr  has  met  this  objection  to  a  considerable  degree 
by  devising  an  apparatus  by  means  of  which  the  total  carbon  may  be 
readily  determined  and  he  has  also  prepared  a  curve  from  which  the 
available  hydrogen  may  be  obtained.  This  curve  is  constructed  on 
the  principle  that  the  available  hydrogen  is  combined  with  volatile 
carbon  in  the  form  of  hydrocarbons  and  that  the  percentage  of  avail- 
able hydrogen,  therefore,  bears  a  fairly  definite  relation  to  the  per- 
centage of  volatile  carbon.  Since  the  latter  is  easily  obtained  by  sub- 
tracting the  fixed  carbon  from  the  total  carbon  it  is  not  difficult  to 
obtain  the  available  hydrogen  from  the  curve. 

Dowling's  Split  Volatile  Ratio  Classification 

In  order  to  avoid  the  necessity  of  making  an  ultimate  analysis 
Dowling1  has  suggested  a  classification  based  on  what  he  calls  the 
" split  volatile  ratio"  This  system  is  adopted  in  order  to  take  into 
account  the  volatile  matter,  which  is  available  for  the  production  of 
heat  and  that  portion  which  is  inert  and  therefore  should  be  placed 
with  the  moisture  as  anti-calorific  material.  The  formula  used  is, — 

Fixed  carbon  -f  i  volatile  combustible     TT7~  , .  ., 

..,  .  — ^ .     When  the  quotients  result- 

Moisture  +  J  volatile  combustible 

ing  from  this  ratio  are  compared  with  those  obtained  from  the  car- 
bon-hydrogen ratio  they  are  found  to  be  almost  equally  satisfactory. 
The  various  coals  may  be  grouped  according  to  this  classification  in 
the  following  order: 

1  Dowling,  D.  B.,  Classification  of  coals  by  the  split  volatile  ratio.  Can.  Min.  Joui. 
pp.  143-146,  April  15,  1908.  Also,  Can.  Geol.  Survey,  Rept.,  No.  1035,  P-  43« 


CLASSIFICATION   ADOPTED    BY   GEOLOGICAL  CONGRESS        113 

Anthracite 15  up 

Semianthracite 13-15 

Anthracite  coal 10-13 

High  carbon  bituminous 6-10 

Bituminous 3 . 5-6 

Low  carbon  bituminous 3-3 . 5 

Lignitic  coal 2 . 5-3 

Lignite 1-2-3.5 

This  split  volatile  ratio  was  adopted  in  part  of  the  following  classi- 
fication of  the  coals  of  the  world  by  the  Twelfth  International  Geol- 
ogical Congress1  and  also  in  a  later  work  by  Bowling  on  the  coal 
resources  of  Canada.2 

Classification  Adopted  by  the  International  Geological  Congress 

CLASS  A 

(1)  Burns  with  short,  blue  flame;  gives  off  3  to  5  per  cent  of  volatile 
combustible  matter. 

._    ,       .        Fixed  carbon 
Fuel  ratio:  —. — —          -  =  12  and  over. 
Volatile  matter 

Calorific  value,  8000  to  8330  calories,  or,  14,500  to  15,000  B.t.u. 
Mean  composition, 

Carbon 93  to  95  per  cent 

Hydrogen 2  to    4       " 

Oxygen  and  nitrogen 3  to    5       " 

(2)  Burns  with  slightly  luminous,  short  flame  and  little  smoke; 
does  not  coke,  and  yields  from  7  to  12  per  cent  of  volatile  matter. 

Fuel  ratio,  7  to  12. 

Calorific  value  generally  8300  to  8600  calories,  or  15,000  to  15,500 
B.t.u. 
Mean  composition, 

Carbon 90  to  93  per  cent 

Hydrogen 4  to  4.5       " 

Oxygen  and  nitrogen 3  to  5.5        " 

CLASS  B 

(i)  Burns  with  short,  luminous  flame  and  yields  12  to  15  per  cent 
volatile  matter;  does  not  readily  coke. 
Fuel  ratio,  4  to  7. 

1  Coal  resources  of  the  world.     Vol.  i,  Toronto,  Canada,  1913. 

*  Coal  fields  and  coal  resources  of  Canada.     Can.  Geol.  Survey,  Mem.  59,  1915. 


114  THE   CLASSIFICATION  OF  COALS 

Calorific  value  generally  8400  to  8900  calories,  or  15,200  to  16,000 
B.t.u. 
Mean  composition, 

Carbon 80    to  90  per  cent 

Hydrogen 4  •  5  to    5 

Oxygen  and  nitrogen 5 . 5  to  12       " 

(2)  Burns  with  luminous  flame  and  yields  from  12  to  26  per  cent 
volatile  matter;   generally  cokes. 

Fuel  ratio,  1.2  to  7. 

Calorific  value  7700  to  8800  calories,  or  14,000  to  16,000  B.t.u. 

Mean  composition, 

Carbon 75    to  90  per  cent 

Hydrogen 4. 5  to  5.5       " 

Oxygen  and  nitrogen 6  to  15        " 

(3)  Burns  freely  with  long  flame;   withstands  weathering  but  frac- 
tures readily  and  occasionally  has  moisture  content  up  to  6  per  cent; 
volatile  matter  up  to  35  per  cent;  makes  porous,  tender  coke. 

Fixed  carbon  +  \  volatile 

! — * =    2 .  C  tO  3 . ^ 

Hygroscopic  moisture  +  J  volatile 

Calorific  value  6600  to  7800  calories,  or  12,000  to  14,000  B.t.u. 

Mean  composition, 

Carbon 70  to  80  per  cent 

Hydrogen 4-5  to    6       " 

Oxygen  and  nitrogen 18  to  20 

CLASS  C 

Burns  with  long,  smoky  flame;  yields  from  30  to  40  per  cent  vola- 
tile matter  on  distillation,  leaving  very  porous  coke.  Fracture 
generally  resinous. 

Calorific  value  6600  to  8800  calories,  or  12,000  to  16,000  B.t.u. 

CLASS  D 

Contains  generally  over  6  per  cent  of  moisture;  disintegrates  on 
drying;  streak  brown  or  yellow;  cleavage  indistinct. 

(i)  Moisture  in  fresh-mined,  commercial  output,  up  to  20  per  cent. 
Fracture  generally  conchoidal. 
Drying-cracks  irregular,  curved  lines. 
Color  generally  lustrous  black,  occasionally  brown. 
Fixed  carbon  +     volatile 


Hygroscopic  moisture  +  \  volatile 


=  1.8  to  2.5 


GRUNER'S   CLASSIFICATION  115 

Calorific  value  5500  to  7200  calories,  or  10,000  to  13,000  B.t.u. 
Average  composition, 

Carbon 60  to    75  per  cent 

Hydrogen 6  to  6 . 5        " 

Oxygen  and  nitrogen 20  to    30 

(2)  Moisture  in  commercial  output  over  20  per  cent.  Fracture 
generally  earthy  and  dull. 

Drying-cracks  generally  separate  along  bedding  planes  and  often 
show  fibrous  (woody)  structure. 

Color  generally  brown,  sometimes  black. 

Calorific  value  4000  to  6000  calories,  or  7000  to  11,000  B.t.u. 

Average  composition, 

Carbon 45  to  65  per  cent 

Hydrogen 6  to  6.8 

Oxygen  and  nitrogen 30  to  45        " 


In  the  above  classification,  letters  are  substituted  for  names.  In 
a  general  way  the  classification  conforms  to  the  nomenclature  used 
in  America,  as  follows: 

AI  =  Anthracite  coal. 

A z  =  Semianthracite  coal. 

Bi  —  Anthracitic  coal  and  high  carbon  bituminous  coal. 

B2  =  Bituminous  coal. 

Bz  =  Low  carbon  bituminous  coal. 

C   =  Cannel  coal. 

DI  =  Lignitic  or  subbituminous  coal. 

Dz  =  Lignite. 

Gruner's   Classification 

In  his  classification  of  French  coals  Gruner1  takes  into  consideration 
the  fixed  carbon  and  volatile  matter  as  well  as  the  constituents  of  the 
ultimate  analysis.  He  also  makes  use  of  the  ratio  of  hydrogen  to 
(oxygen  +  nitrogen).  No  provision  is  made  for  lignite,  subbitumi- 
nous coal,  or  cannel.  The  following  table  is  a  slightly  abbreviated 
compilation  of  Gruner's  tables.  As  previously  mentioned  the  term 
"houille"  in  French  corresponds  to  bituminous  coal  in  America,  and 
"charbon"  is  the  general  term  used  for  coal. 

1  Gruner,  E.,  and  Bousquet,  G.,  Atlas  general  des  houilleres.  Deuxieme  partie, 
Texte  p.  16,  1911. 


n6 


THE   CLASSIFICATION  OF  COALS 


Class  or  type  of  coal 
and  commercial 
name  in  France 

Proportion  oi 
coke  in  100 
parts  of  pure 
coal 

Proportion  of 
volatile  matter 
in  loo  parts  of 
pure  coal 

Nature  and  ap- 
pearance of 
coke 

Real  calorific 
power 

Industrial  cal- 
orific power. 
Water  at  o° 
vaporised  at 
112°  by  i  kgm. 
of  pure  coal 
burned 

Per  cent 

Per  cent 

Calories 

Kgms.  of  water 

i.  Houilles     se- 
ches  (dry) 
&  longue 
flamme. 
Houilles  flam- 
bantes. 

55-60 

45-40 

Powdery    or 
slightly 
fused. 

8000-8500 

6.70-7.50 

2.  Houilles 
grasses    (fat) 
a  longue 
flamme. 
Charbons  a 
gaz. 

60-68 

42-32 

Completely 
agglomer- 
ated and 
very  often 
fused. 

8500-8800 

7.60-8.30 

3.  Houilles 
grasses    (fat) 
proprement 
dites.   Char- 
bons de  forge 
et  Houilles 
marechales 
(smiths). 

68-74 

32-26 

Fused  and 
more  or  less 
swollen. 

8800-9300 

8.40-9.20 

4.  Houilles 
trasses    (fat) 
courte 
flamme. 
Charbons  a 
coke. 

74-82 

26-18 

Fused,  com- 
pact. 

9300-9600 

9.20-IO.OO 

5.  Houilles 
maigres  (lean) 
ou    anthracit- 
euses  char- 
bons  demi- 
gras.  Char- 
bons quart- 
gras. 

82-90 

I8-IO 

Slightly 
fused,  very 
often  powd- 
ery. 

9200-9500 

9.00-9.50 

6.  Anthracites. 
Charbon 
maigre  (lean) 
anthracite. 

90-92 

10-8 

Powdery, 
often  de- 
crepitated. 

9000-9200 

9.00 

GRUNER'S   CLASSIFICATION 


117 


Carbon 

Hydrogen 

Oxygen  anc 
Nitrogen 

.   0  +  N 

Designation  in 
Germany 
(Ruhr  Basin) 

Designation  in 
Belgium 

Designation  in 
England 

Ratio     H 

Per  cent 
I.   70-80 

Per  cent 

Percent 

5-5-4-5 

I9-5-I5-5 

Between 
4  and  3  • 

Flamm- 
Kohle 

Flenus 
sees 

Splint  coal 

2.    80-85 

5-8-5-0 

14.2-10.0 

Between 
3  and  2 

Gas-Kohle 

Flenus 
gras  ou 
Mons 

Gas  coal 

3-    84-89 

S-o-5-5 

11.0-5.5 

Between 
2  and  i 

Fett-Kohle 

Caking  coal 

4.    88-91 

5-5-4-5 

6-5-4-5 

Nearly  i 

Fett-Kohle 

Charbons 
durs  ou 
Charleroi 

Steam  coal 

5-  90-93 
6.  93-95 

4-5-4-0 
4  .  0-2  .  o 

5-5-3-0 

Less  than 

i 

Mager- 
Kohle 

3-o 

1-0.5 

Anthrazit 

Anthracite 

Anthracite 

Il8  THE    CLASSIFICATION   OF   COALS 

A  number  of  experiments  have  shown  that  the  lean  (maigre)  coals 
are  almost  insoluble  in  the  ordinary  solvents  such  as  aniline  while 
there  is  an  increasing  proportion  of  the  fuel  soluble,  in  passing  from 
the  lean  to  the  fat  (gras)  coals. 

Ashley 's  Use  Classification 

A  classification  has  recently  been  suggested  by  Ashley1  which  is 
intended  primarily  for  the  use  of  the  person  engaged  in  the  coal 
business  and  which  he  designates  as  a  "Use  Classification."  The 
main  factors  on  which  this  classification  are  based  are  two  ratios, 
the  first  being  the  ratio  of  the  fixed  carbon  to  volatile  matter  and  moist- 

F  c 

ure  combined  — —       '          and  the  second  the  fuel  ratio  and  the 
V.m.  +  rizU 

fixed-carbon-moisture  ratio  (F.c.m.  ratio).  A  double  ratio  is  thus 
made  use  of  as  in  some  of  the  previous  classifications  described.  The 
higher-rank  coals  are  distinguished  by  their  fuel  ratio  and  the  lower 
ranks  by  the  ratio  of  the  moisture  "as  received"  to  fixed  carbon. 
These  ratios  are  chosen  because  in  the  higher  ranks  of  coal  the  moist- 
ure changes  little  and  the  volatile  matter  much  in  relation  to  the 
fixed  carbon  when  one  rank  of  coal  is  changed  to  another  higher  in  the 
scale  by  geological  processes,  while  in  the  lower  ranks  there  is  a  larger 
proportional  change  in  the  moisture  than  in  the  volatile  matter  with 
respect  to  the  fixed  carbon.  The  physical  properties  are  also  taken 
into  consideration  since  they  depend  largely  upon  the  genesis  of  the 
coal  and  must  therefore  be  closely  related  to  the  chemical  properties. 
For  example  cannel  coal  differs  greatly  from  ordinary  bituminous 
coal  because  of  its  different  origin.  The  woody  character  of  low- 
grade  coals  is  also  considered. 

A  new  departure  in  this  classification  is  the  adoption  of  locality 
names  for  certain  ranks  and  grades  of  coal.  The  coal  of  a  distinctive 
grade  from  a  well-known  mining  locality  takes  the  name  of  the  lo- 
cality with  the  name  changed  so  as  to  end  in  ite.  As  examples, 
Pocahontas  coal  would  be  known  on  the  market  as  Pocahontite  and 
Hocking  Valley  coal  as  Hockingite.  In  addition  to  the  use  of  these 
terms  for  coal  from  those  fields  the  names  might  be  applied  to  the 
same  grade  of  coal  from  other  localities,  thus  adopting  the  use  of 
locality  names  as  they  are  used  in  mineralogy. 

1  Ashley,  G.  H.,  A  use  classification  of  Coal.  Trans.  Amer.  Inst.  Min.  Met.  Eng. 
LXIII,  p.  782, 1920. 


ASHLEY'S   USE   CLASSIFICATION 


119 


The  following  tables  show  examples  of  the  application  of  these 
ratios  to  the  analyses  of  various  typical  coals  throughout  the  country. 
The  first  table  shows  the  ratio  of  fixed  carbon  to  volatile  matter  and 
moisture  combined,  and  the  second  the  fuel  ratio  and  fixed-carbon- 
moisture  ratio. 

RATIO  OF  FIXED  CARBON  TO  VOLATILE  MATTER  AND 
MOISTURE  COMBINED 


(  ~  —  F',°'1J 
\V.m.  +  H 


Coal 

Ratio 

Coal 

Ratio 

Anthracite        .  . 

IO    7  4- 

Saint  Clair  Co.,  111.  coal 

o  96 

Bernice  coal 

6  8 

Sangamon  Co.,  111.  coal  

o  84 

Brushy  Mountain,  Va.  coal  .  .  . 
Pocahontas  coal  .    . 

4.8 

7  .7 

Grundy  Co.,  111.  coal  
Sheridan,  Wyo.  coal  

0.78 

o  68 

Sewell,  New  River,  coal  

2.8 

Carney,  Wyo.  coal  

o  62 

Connellsville  coal  

2  .O 

Gillette,  Wyo.  coal  

o.  <c6 

Pittsburgh  coal  

1.6 

Wood  Co.,  Tex.  lignite  

O  .  cjO 

Beaver  River,  Pa.  coal  

I  .2 

Houston  Co.,  Tex.  lignite  

0.4-? 

Gallatin  Co.,  111.  coal  

I  .09 

Williston,  N.  Dak.  lignite  

0.37 

FUEL  RATIO  AND  FIXED-CARBON-MOISTURE  RATIO 
(F.c.m.  ratio.) 


Coal 

Fuel 
ratio 

Carbon 
moisture 

Coal 

Fuel 
ratio 

Carbon 
moisture 

Anthracite  

10+ 

io+(3o±) 

Saint  Clair  Co.,  111.  .  . 

1  .4- 

4  O-6  O 

Bernice  

7—10 

IO+(27±) 

Sangamon  Co.,  111.  .  . 

I  .4- 

2  .  "?—  4  O 

Brushy  Mountain, 
Va 

r—  7 

IO+(26+) 

Grundy  Co  ,  111. 

I    4.— 

2    O—  2    ^ 

Pocahontas  . 

•j    e-  e 

IO+(24    O 

Sheridan,  Wyo. 

I    4.— 

I    7—2    O 

Sewell               

2    <—  3    «C 

io+(23) 

Carney,  Wyo. 

I    4— 

I    4.—  I    7 

Connellsville  

I    85-2    * 

IO-h(2T    5) 

Gillette,  Wyo  

I    4- 

I    O   —  I    4. 

Pittsburgh  

I  .4-1.85 

io-}-(i9  .5) 

Wood  Co.,  Tex  

T    4— 

o  85-1  oo 

Beaver  River,  Pa. 
Gallatin  Co.,  111... 

1.4- 

i-4- 

io+(i7) 
6  .0-10.0 

Houston  Co.,  Tex  
Williston,  N.  Dak..  .. 

1.4- 
1.4- 

o  .  65-0  .  85 

0.5    -0.65 

From  these  tables  it  is  seen  that  the  lignites  fall  between  0.5  and 
i  in  the  fixed-carbon-moisture  ratio,  most  of  the  subbituminous 
coals  between  i  and  2  and  the  bituminous  coals  between  2  and  io+. 
Above  this  point  the  fuel  ratio  is  used  as  a  basis  of  separation. 

From  a  physical  standpoint  all  coals  are  first  divided  into  those 
of  compact  texture  and  those  of  woody,  fibrous,  or  earthy  texture. 
Those  of  compact  texture  are  next  divided  into  an  anthracite  class 
and  a  bitumite  class.  The  anthracite  class  has  a  fuel  ratio  of  7+  and 


120  THE   CLASSIFICATION  OF  COALS 

a  non-luminous  flame,  and  the  bitumite  class  a  fuel  ratio  of  less  than 
7  and  a  luminous  flame.  The  latter  class  includes  the  bituminous 
and  subbituminous  coals. 

The  anthracites  are  further  divided  into  true,  hard  anthracites  with 
conchoidal  fracture,  high  specific  gravity  and  submetallic  luster 
and  the  soft  anthracites  with  semi-cubic  fracture  and  low  specific 
gravity  —  such  as  the  so-called  anthracite  at  Bernice,  Sullivan  Co., 
Pa.  The  dividing  line  between  these  two  groups  is  a  fuel  ratio  of  10. 

The  bitumites  are  divided  first  into  those  with  a  B.t.u.  value  of 
over  14,300  and  those  with  a  value  less  than  that  when  calculated  on 
a  coal  free  of  moisture,  ash  and  sulphur.  The  calculation  is  made 
from  the  following  formula: 

B.t.u.  (ash-,  moisture-,  B.t.u.  (coal  as  received)  —  40  S. 

sulphur-free)  100  —  (moisture  +  ash  +  sulphur) 

The  higher  rank  bitumites  are  divided  into  the  Virginites,  or  so-called 
smokeless  coals,  having  a  fuel  ratio  between  2.5  and  7,  and  those 
with  a  fuel  ratio  below  2.5.  The  former  have  a  short  to  medium  flame 
and  the  latter  a  long  flame. 

The  Virginites  are  divided  into  three  types  having  fuel  ratios 
respectively  between  5  and  7;  between  3.5  and  5;  and  between  2.5 
and  3.5.  The  first  type  is  a  non-caking  coal  while  the  other  two  are 
caking  coals.  The  Pocahontas  type  has  a  fuel  ratio  of  3.5-5  and  the 
Sewell  type  a  ratio  of  2.5-3.5.  The  other  group  of  the  high  grade 
bitumites  is  divided  into  the  caking  or  steam  coals  and  the  non- 
caking  or  household  coals.  The  caking,  long-flamed  coals  are  again 
divided  into  two  groups  based  on  a  fuel  ratio  of  i  .4.  Those  above  this 
figure  are  called  the  Pennsites  from  their  abundance  in  Pennsylvania. 
The  Pennsites  are  again  divided  into  Connellsite  with  a  fuel  ratio  of 
1.85  or  more  and  Pittsite  with  a  fuel  ratio  between  1.4  and  1.85. 
These  names  are  taken  from  the  Connellsville  and  Pittsburgh  dis- 
tricts. 

Those  coals  with  a  fuel  ratio  below  1.4  and  a  fixed-carbon-moisture 
ratio  of  more  than  6  are  called  Ohioites  and  those  with  a  similar 
fuel  ratio  but  with  the  other  ratio  less  than  6,  but  still  in  the  bitumite 
class,  are  called  Illinoites.  The  Ohioites  are  again  divided  into  the 
Belmontites  with  a  fixed-carbon-moisture  ratio  of  more  than  10 
and  Hockingites  with  a  ratio  between  6  and  10.  The  Illinoites  which 
are  high-moisture  coals  are  also  subdivided. 


ASHLEY'S  USE   CLASSIFICATION 


121 


The  non-caking  or  household  coals  are  divided  into  two  groups, 
the  splintites  and  the  cannellites,  wh  ch  are  separated  on  a  physical 
basis  as  their  structure  and  fracture  are  quite  different.  The  lower- 
rank  bituminous  coals  with  a  fuel  value  of  less  than  14,300  B.t.u. 
on  the  ash-,  moisture-  and  sulphur-free  basis  are  divided  into  two 
groups  according  to  their  weather  resisting  properties. 

For  the  convenience  of  those  persons  who  purchase  coal  by  wire 
Ashley  has  suggested  letters  to  designate  the  various  ranks  of  coal 
and  the  grades  in  those  ranks.  The  table  of  letter  abbreviations  for 
the  grades  is  as  follows : 


Ash  per  cent 

Sulphur  per  cent 

Fusibility  of  ash,  degrees  F. 

VI  =  very  low 

0-  4 

0.00-0.75 

Less  than  2200 

/  =  low 

4-  8 

0-75-1-5 

2200-2400 

m  =  medium 

8-12 

i-5  -2.5 

2400-2600 

h  =  high 

I2-2O 

2-5  -4 

2600-2800 

Vh  =  very  high 

2O+ 

4  + 

2800+ 

The  letters  a,  s,  and  /  also  stand  for  ash,  sulphur  and  fusibility  re- 
spectively. The  fusibility  of  the  ash  is  an  important  factor  in  the 
heating  quality  of  the  coal  because  of  the  effect  it  may  have  in  clog- 
ging the  grates,  and  it  should  be  given  serious  consideration. 

This  classification  may  appear  complicated  to  the  average  man 
dealing  in  coal;  there  will  be  many  exceptions  to  the  classes  made  and 
people  long  accustomed  to  such  terms  as  Pocahontas  coal  may  at  first 
object  to  the  use  of  Pocahontite  for  coal  from  another  region;  yet 
there  are  a  number  of  features  in  this  classification  wh'ch  commend  it. 
One  important  one  is  the  fact  that  a  proximate  analysis  furnishes  the 
necessary  data  for  making  the  computations 

After  a  review  of  all  available  classifications  of  coal  it  must  be  con- 
cluded that  no  one  classification  so  far  suggested  meets  with  general 
approval.  Some  of  the  classifications  are  very  satisfactory  in  com- 
bining the  physical  and  chemical  properties  of  certain  of  the  coals  so 
that  they  coincide  with  the  names  familiar  to  the  public,  and  firmly 
established  in  the  coal  trade.  Others  are  applicable  to  certain  other 
coals  and  it  seems  probable  that  when  the  number  of  analyses  has 
been  greatly  increased  and  our  knowledge  of  the  controlling  chemical 
factors  in  coals  has  become  somewhat  more  advanced  it  will  be  possible 
to  formulate  a  classification  which  will  be  workable  under  most  con- 


122  THE   CLASSIFICATION  OF   COALS 

ditions  at  least.  Some  of  the  classifications  may  now  be  applied  to 
certain  regions  with  satisfactory  results,  but  it  is  improbable  that  any 
one  will  ever  be  applicable  to  all  kinds  of  coals  from  all  districts, 
owing  to  the  great  diversity  of  physical  and  chemical  characters 
resulting  from  the  variations  in  the  vegetal  matter  from  which  coals 
have  been  derived  and  in  the  variable  geological  conditions  under 
which  they  have  been  developed.  The  classifications,  therefore, 
which  require  more  than  two  factors  as  a  basis  for  determination  of 
a  type  come  nearer  satisfying  the  fundamental  requirements  than 
those  which  are  based  on  a  ratio  between  only  two  constituents,  and 
from  a  practical  standpoint  the  making  of  ultimate  analyses  by  the 
present  chemical  methods  is  to  be  avoided  when  possible. 


CHAPTER  VI 
THE   ORIGIN   OF   COAL 

Introduction 

In  the  earlier  days  of  geological  science  a  few  theorists,  searching 
for  some  abstruse  explanation  for  the  origin  of  coal  seams  suggested 
that  they  were  intruded  into  the  enclosing  strata  as  bituminous  de- 
posits of  igneous  origin  in  the  same  manner  that  sills  of  igneous  rock 
are  injected  between  beds  of  sediments.  Patrin  regarded  the  seams 
as  extrusions  of  bituminous  matter  on  the  sea  bottom.  So  definite 
is  the  evidence,  however,  that  all  coal  has  resulted  from  the  alteration 
of  vegetal  matter  in  some  form,  that  a  theory  of  origin  based  on  any 
other  premise  may  be  dismissed  without  consideration.  Any  one 
questioning  this  conclusion  has  but  to  observe  the  transition  from 
peat  to  lignite  and  from  lignite  to  bituminous  coal,  with  a  gradual 
decrease  in  the  distinctness  of  the  plant  remains  in  passing  from  the 
lower  to  the  higher  grades  of  coal,  to  be  convinced  regarding  this 
matter.  Many  of  even  the  hard  coal  seams  contain  remnants  of 
trees  completely  changed  to  coal  but  retaining  the  markings  of  the 
bark  and  other  woody  structures.  The  modern  application  of  the 
microscope  to  the  study  of  those  coals  which  show  to  the  naked  eye 
no  evidence  of  plant  remains  reveals  the  spores,  the  fragments  of 
resin  and  the  modified  woody  tissue  of  the  vegetation  which  formed 
the  coal. 

Although  it  is  almost  universally  agreed  that  all  the  varieties  of 
coal  originated  from  vegetal  matter  there  is  much  difference  of  opinion 
regarding  its  mode  of  accumulation  into  such  great  bodies  as  those 
which  gave  rise  to  the  coal  seams.  There  is  also  a  great  divergence 
of  opinion  among  geologists  and  paleobotanists  regarding  the  proces- 
ses by  means  of  which  the  vegetation  has  been  brought  into  the  form 
of  brown  coal,  bituminous  coal,  or  anthracite,  in  which  it  is  now 
found. 

123 


124  THE  ORIGIN  OF  COAL 

Theories  for  the  Accumulation  of  the  Vegetal  Matter1 

There  are  two  main  theories  for  the  accumulation  of  the  vegetal 
matter  giving  rise  to  coal  seams,  and  there  are  two  schools  of  geologists 
supporting  these  theories.  One  school  contends  that  the  plant 
remains  accumulated  in  situ,  that  is,  where  the  vegetation  grew  and 
fell,  and  the  deposit  is  said  to  be  autochthonous  in  origin.  The  other 
considers  that  the  deposit  is  allochthonous ,  that  it  has  accumulated  as 
a  result  of  the  transportation  of  the  vegetal  matter  by  water.  Ac- 
cording to  the  latter  theory  the  fragments  of  plants  have  been  carried 
by  streams  and  deposited  on  the  bottom  of  the  sea  or  in  lakes,  in 
much  the  same  manner  as  any  other  sediment  would  be  carried,  and 
allowed  to  settle  to  the  bottom  to  build  up  strata  which  later  become 
compressed  into  solid  rock. 

The  evidence  favoring  the  in  situ  or  autochthonous  origin  of  the 
deposit  may  be  summed  up  as  follows:  (i)  There  are  large  accumu- 
lations of  vegetal  matter  forming  in  swamps  at  the  present  time, 
some  of  which  are  on  a  scale  approaching  those  which  gave  rise  to 
coal  seams  of  considerable  extent.  (2)  The  purity  of  the  coal,  or 
its  relative  freedom  from  mineral  matter,  suggests  the  collection  of 
the  vegetation  in  swamps  rather  than  in  deposits  where  it  has  been 
transported  with  other  sediments.  The  periods  of  high  water  when 
the  greatest  amount  of  vegetation  is  transported  are  also  those  when 
most  mineral  matter  is  carried.  (3)  Numerous  tree  trunks  with 
their  roots  firmly  embedded  in  the  underlying  clays  occur  in  the  coal 
seams  and  in  some  cases  the  rootlets  pierce  fragments  of  buried  wood 
in  the  clays.  (4)  The  topographic  conditions  under  which  the  large 
coal  fields  formed  were  like  that  of  a  land  surface  near  the  critical  level 
(that  is,  near  sea  level),  and  a  slight  sinking  of  the  land  would  permit 
the  sea  to  transgress  over  it  or,  in  basins  removed  from  the  sea,  per- 
mit sediment  to  be  washed  into  the  basin  from  adjoining  lands. 
(5)  Old  soils  on  which  the  trees  grew  lie  beneath  the  seams  in  some 
places.  (6)  Such  an  accumulation  could  not  take  place  in  the  open 
sea  and  estuaries  are  not  in  very  favorable  locations  because  of  the 
immense  amount  of  mud  usually  carried  into  them.  (7)  The  arrange- 
ment of  various  portions  of  plants  with  respect  to  one  another  is  not, 
as  a  rule,  that  of  transported  material.  (8)  The  lenses  of  cannel  in 

1  For  summary  of  theories  see  "The  formation  of  coal  beds,"  by  J.  J.  Stevenson. 
Proc.  Amer.  Phil.  Soc.,  Vol.  50,  pp.  1-116,  1911. 


THEORIES   FOR  ACCUMULATION  OF  VEGETAL  MATTER        125 

bituminous  coal,  or  bands  along  the  upper  surface  of  bituminous  coal 
seams,  indicate  patches  of  open  water  in  swamps  where  spores  would 
collect  in  great  quantities  rather  than  deposits  forming  part  of  an 
ordinary  sedimentary  formation.  (9)  The  lenses  and  bands  of  "  min- 
eral charcoal"  suggest  higher  portions  in  the  swamp  exposed  to  weath- 
ering and  more  extensive  rotting  than  that  undergone  by  the  remainder 
of  the  vegetation  in  the  swamp.  If  this  charcoal  represents  the 
remnant  of  burned  wood  transported  to  open  water  as  some  have 
suggested,  it  could  scarcely  have  the  distribution  which  it  usually 
has  in  the  coal  seams. 

In  favor  of  the  transportation  or  allochthonous  theory  there  are  the 
following  factors:  (i)  Enormous  quantities  of  timber  are  rafted 
down  streams  in  regions  of  virgin  forest.  (2)  In  some  modern  deltas 
beds  of  peat  and  brown  coal  have  been  found.  (3)  Coal  beds  are 
often  associated  with  marine  fossils  which  occur  in  the  strata  im- 
mediately above  or  below  the  seams  of  coal.  (4)  The  rocks  associ- 
ated with  the  coal  are  distinctly  sedimentary  and  the  seams  appear 
to  constitute  a  part  of  a  regular  sedimentary  series,  usually  showing 
an  increasing  fineness  in  the  particles  of  sediment  in  the  rocks  under- 
lying the  seam  as  the  seam  is  approached.  (5)  The  fire-clay  beds 
commonly  found  beneath  coal  seams  are  not  necessarily  clays  on  which 
forests  grew,  as  formerly  supposed,  because  similar  clays  have  been 
found  in  marine  formations  unassociated  with  coal.  (6)  It  is  diffi- 
cult to  determine  in  many  cases  whether  a  stump  of  a  tree  is  located 
where  it  grew  or  whether  it  has  been  transported  to  its  present  lo- 
cation and  gradually  buried  by  clay  or  sand  which  settled  around  it, 
while  resting  upright  on  the  bottom  of  the  basin.  (7)  Trees  have 
been  found  with  their  tops  headed  downward.  (8)  The  large  num- 
bers of  spores  grouped  in  the  coal  in  some  seams  indicates  their  ability 
to  float  about  freely  and  collect  in  masses.  (9)  The  presence  of 
fish  remains  in  coal,  especially  the  cannel  coal  of  England,  suggests 
considerable  open  water  where  the  vegetation  accumulated.  (10) 
It  would  appear  to  be  difficult  for  large  trees  to  root  in  such  an  enor- 
mous depth  of  vegetal  matter  as  that  necessary  to  produce  some  of 
our  thickest  coal  seams. 


126  THE  ORIGIN   OF   COAL 

Historical  Sketch  of  the  Development  of  the  Theories  for  the 
Origin  of  Coal 

As  early  as  the  year  1778  Buffon1  recognized  the  vegetal  origin  of 
coal  and  gave  it  the  name  charbon  de  terre,  the  term  still  frequently 
used  in  France.  In  the  same  year  Von  Beroldingen2  very  intelli- 
gently expounded  the  in  situ  origin  of  the  vegetation  in  a  peat-bog, 
its  burial  and  its  transformation  from  peat  into  the  various  types 
of  coal.  These  writers  were  followed  by  many  who  had  more  or  less 
hazy  and  highly  theoretical  views  regarding  the  origin  of  coal.  Even 
Darwin  seemed  to  regard  some  of  the  coal  beds  as  bituminous  dis- 
tillations from  vegetal  matter  capable  of  migration  from  one  rock 
horizon  to  another. 

In  the  year  1831  MacCulloch  published  a  work3  in  which  he  sup- 
ported the  peat-to-coal  theory.  He  pointed  out  that  the  plants 
forming  the  peat  were  of  terrestrial  type  and  that  they  grew  in  swamps. 
Three  years  later  Marinnott  recognized  the  prevalence  of  an  under- 
day  with  coal  seams  but  stated  that  there  could  be  no  genetic  con- 
nection between  the  coal  and  the  clay  because  he  failed  to  find  roots 
in  the  clay.  A  little  later  Buckland4  described  how  the  vegetal  mat- 
ter was  transported  and  he  expounded  the  drift  origin  of  the  deposits. 
Although  Witham5  had  probably  made  the  first  microscopic  studies 
of  coal  in  1833  it  remained  for  Link6  to  extend  this  work  five  years 
later  and  apply  his  results  to  the  origin  of  coal.  He  concluded  that 
coal  was  developed  from  peat  because  of  the  presence  of  various 
vegetal  materials  in  it  and  that  the  vegetation  accumulated  in  place. 
In  1841  Logan7  stated  that  from  his  observations  underclays  were 

1  Buffon,  L.  de.,  Histoire  natureJle,  generate  et  particuliere  Sonnini  Edn.  Tome  9  me, 
Paris. 

2  Von   Beroldingen,   Franz.,   Beobachtungen,   zweifel  und   Fragen,  die  Mineralogie 
iiberhaupt  und  insbesondere  ein  natiirliches  Mineral  System  betreffend;   Erster  Versuch, 
i778. 

3  MacCulloch,  J.,  A  System  of  geology  with  a  theory  of  the  earth,  Vol.  II. 

4  Buckland,  W.,  Geology  and  mineralogy  considered  with  reference  to  natural  theology, 
Phila.  1837. 

5  Witham,  H.,  On  the  Internal  structure  of  fossil  vegetables  found  in  the  carboniferous 
and  oolitic  deposits  of  Great  Britain,  1833. 

6  Link,  F.,  Uber  den  Ursprung  der  Steinkohlen  und  Braunkohlen  nach  mikroskopischen 
Untersuchungen.     Abhandlungen  d.  k.  Preuss,  Akad.  Wiss.  Berlin  pp.  33-34,  1838. 

7  Logan,  W.  E.,  On  the  character  of  the  beds  of  clay  lying  immediately  below  the  coal 
seams  of  South  Wales.     Proc.  Geol.  Soc.  London,  Vol.  Ill,  1841. 


HISTORICAL   SKETCH  OF  DEVELOPMENT  OF  THEORIES 

characteristic  of  all  coal  seams  and  that  from  the  presence  of  Stig- 
maria  in  these  clays  the  vegetation  must  have  consisted  chiefly  of 
this  species  which  grew  on  these  clays.  Two  years  later  Rogers1 
published  a  very  comprehensive  statement  of  the  results  of  his  ob- 
servations. He  concluded  that  the  Pittsburgh  seam  extends  over 
at  least  14,000  square  miles  and  that  when  isolated  areas  where  it 
occurs  are  added  the  total  area  could  not  be  far  from  30,000  square 
miles.  He  stated  that  he  failed  to  see  how  beds  of  such  extent  and 
purity  could  have  been  formed  from  drifted  vegetation  and  he  be- 
lieved that  they  were  formed  in  swamps  on  great  marginal  plains 
subjected  to  gradual  subsidence.  He  considered  the  underclays  as 
very  common  and  Stigmaria  as  almost  always  present  in  them,  often 
preserving  its  fibrous  processes.  Another  important  point  that  he 
brought  out  was  that  the  roof  was  different  from  the  sole  formation 
and  that  the  roof  sandstones  showed  evidence  of  strong  currents. 

From  a  study  of  Russian  coals  Murchison2  favored  the  drift  theory 
but  he  also  preferred  the  in  situ  theory  for  some  of  the  English  coal 
seams  where  the  underclays  represent  old  soils  on  which  Sigillaria 
grew.  Le  Conte3  favored  the  in  situ  theory  because  of  the  purity  of 
the  coal  and  the  preservation  of  the  delicate  portions  of  the  vegetal 
matter.  He  believed  that  the  vegetation  grew  in  bogs  around  the 
mouths  of  large  rivers.  Jukes4  favored  the  drift  theory  because  of 
the  "rock  faults"  and  frequent  alternations  of  barren  rock  and  coal. 
He  believed  that  the  materials  were  sorted  on  the  basis  of  specific 
gravity.  On  the  other  hand  Dawson  concluded  from  a  microscopic 
study  of  coal  and  an  extensive  investigation  of  the  South  Joggins 
area  in  Nova  Scotia  that  the  vegetation  grew  where  it  was  accumul- 
ated because  of  the  numerous  examples  of  standing  trunks,  and  the 
roots  in  place.  He  considered  that  the  coal  consisted  chiefly  of  bark 
and  similar  materials  with  spores  as  a  very  minor  constituent.  He 
also  regarded  the  irregularities  in  the  floor  of  the  seams  as  charac- 
teristic of  the  inequalities  seen  in  swamps  of  the  present  day.  Steven- 

1  Rogers,  H.  D.,  An  inquiry  into  the  origin  of  the  appalachian  coal  strata,  bituminous 
and  anthracite,  Repts.  of  Amer.  Ass.  of  Geologists  and  Naturalists,  Boston,  1843. 

2  Murchison,  R.  I.,  The  geology  of  Russia  in  Europe  and  the  Ural  Mountains,  Vol. 
I,  p.  112,  1845. 

3  Le  Conte,  J.,  Lectures  on  coal.     Ann.  Rept,  Smithsonian  Inst.,  p.  131,  1858. 

4  Jukes,  J.  B.,  The  South  Staffordshire  coal  field.     Memoirs  Geol.  Survey  of  Great 
Britain,  2  ed.  London  1859. 


128  THE  ORIGIN  OF  COAL 

son,1  Andrews,2  and  Newberry,3  as  a  result  of  their  studies  in  Penn- 
sylvania, Ohio  and  West  Virginia  strongly  support  the  in  situ  theory. 
Dana  considered  that  the  coal  was  made  up  of  all  parts  of  the  trees 
and  that  it  accumulated  in  marshes.  Mietzsch4  was  opposed  to  the 
transport  theory  and  described  the  sunken  forests  near  the  coast  off 
Rotterdam  as  illustrative  of  buried  peat  deposits  found  in  situ.  In 
1878  Lesley5  described  how  cannel  lenses  occur  in  pools  on  the  mass  of 
vegetation  which  formed  the  coal  seam  and  pointed  out  the  significant 
fact  that  if  the  coal  deposits  were  not  formed  in  a  continuously  sub- 
siding area  it  would  have  been  impossible  for  the  many  thousands  of 
feet  of  shallow  water  deposits  filling  the  Appalachian  trough  to  have 
been  laid  down  beneath  the  Coal  Measures.  He  also  believed  that 
the  underclays  represented  the  finer  particles  of  rock  sorted  out  of 
the  coarse  sandstones  and  conglomerates  and  concluded  that  where 
underclays  were  thick  they  should  therefore  be  associated  with  ex- 
tensive sandstone  strata.  Grand' Eury6  seems  to  have  favored  a 
sort  of  combined  in  situ  and  drift  theory  as  he  believed  the  vegetation 
collected,  suffered  considerable  decomposition,  and  was  then  washed 
from  the  land  into  the  standing  water  where  it  was  buried.  He 
regarded  the  mineral  charcoal  as  wood  dried  in  the  air.  An  objection 
was  raised  to  the  in  situ  theory  because  the  roots  of  the  trees  do  not 
penetrate  the  coal  but  spread  out  over  it  at  the  top  of  the  seam  in- 
dicating that  they  cannot  exist  in  a  mass  of  decomposing  vegetal 
matter.  It  is  well  known,  however,  that  this  objection  is  overcome 
by  observation  of  a  modern  peat-bog  or  swamp.  Griiner7  objected 
to  the  transportation  of  the  vegetal  matter  chiefly  because  of  the 
freedom  of  the  coal  from  mineral  sediment.  He  was  strongly  in 
favor  of  accumulation  in  place. 

In  the  year  1883  Von  Gumbel8  published  an  excellent  discussion 

1  Stevenson,  J.  J.,  The  upper  coal  measures  west  of  the  Allegheny  Mountains.  Ann 
Lye.  Nat.  Hist.  N.  Y.,  Vol.  X,  p.  226,  1873. 

Andrews,  E.  B.,  Geol.  Survey  of  Ohio.     Vol.  I,  Pt.  I,  1873. 

Newberry,  J.  S.,  Geol.  Survey  of  Ohio,  Vol.  II,  Pt.  I,  1874. 

Mietzsch,  H.,  Geologic  der  Kohlenlager,  1875. 

Lesley,  J.  P.,  Second  Geol.  Survey  of  Pa.,  1878. 

Grand'Eury,  Memoire  sur  la  formation  de  la  houille.  Ann.  des  Mines  Ser.  8,  Tome 
I,  1882. 

Griiner,  L.,  Bassin  houiller  de  la  Loire,  1882. 

Von  Gumbel,  C.  W.,  Bertrage  zur  Kenntniss  der  Texturverhaltnisse  der  Mineral- 
kohlen.  Sitzungs  d.  Math.  Phys.  Klasse  k.  b.  Akad.  Wiss.,  Vol.  13,  p.  113,  1883. 


HISTORICAL  SKETCH  OF   DEVELOPMENT  OF  THEORIES         1 29 

of  his  microscopic  and  field  observations.  He  treated  fragments  of 
coal  with  potassium  chlorate,  nitric  acid  and  later  with  ammonia. 
He  then  washed  them  with  absolute  alcohol,  thus  employing  a  system 
very  similar  to  that  used  in  recent  years.  He  showed  that  even  the 
" stove"  coal  is  made  up  of  the  various  fragments  of  plant  debris, 
some  of  which  are  much  more  easily  decomposed  and  much  less  dur- 
able than  others.  He  concluded  that  different  varieties  of  coal  may 
result  because  of  differences  in  the  kinds  or  parts  of  plants,  because 
of  differences  in  chemical  and  mechanical  conditions,  or  in  the  ex- 
ternal conditions  during  transformation.  He  first  used  the  terms 
allochthonous  and  autochthonous  respectively  to  designate  accumu- 
lation by  transportation  and  accumulation  in  place.  He  regarded 
the  interstratification  of  coal  and  distinct  sediments  as  a  strong 
factor  in  favor  of  those  who  support  the  drift  theory  but  he  felt  that 
other  evidence,  —  especially  the  similarity  between  vegetation  in 
modern  coastal  swamps,  subject  to  submergence  by  the  sea,  and  the 
peat  deposits  which  gave  rise  to  the  coal,  —  substantiated  the  autoch- 
thonous origin  of  the  coal. 

As  a  champion  of  the  drift  theory  probably  no  one  man  has  pro- 
duced more  convincing  evidence  in  its  favor  than  has  Fayol,1  a  mining 
engineer,  who  made  elaborate  observations  in  the  basin  of  Commentry 
in  central  France.  He  further  supported  some  of  his  conclusions  by 
laboratory  experiments  and  as  a  result  of  his  work  a  number  of  men 
were  led  to  accept  his  opinions,  among  them  the  well-known  French 
scientists,  A.  de  Lapparent  and  B.  Renault.  He  considered  that  the 
vegetation  grew  on  high  lands  surrounding  a  deep  lake  and  was  washed 
into  this  body  of  water  where  it  was  deposited  in  a  delta  along  with 
sandstones  and  conglomerates.  The  distinct  delta  deposits,  the 
presence  of  abundant  fish  remains  in  associated  shales,  and  the  pres- 
ence of  trees  with  their  tops  headed  downward  are  all  taken  as  dis- 
tinct evidences  of  the  transportation  of  the  vegetation.  Many  of 
these  arguments  are  successfully  refuted  by  Stevenson2  who  later 
studied  the  area  and  who  claimed  that  nothing  but  a  series  of  cloud- 
bursts could  tear  the  vegetation  from  the  surrounding  lands  if  it  were 
as  dense  as  necessary  to  produce  the  coal  seams  under  discussion  in 

1  Fayol,  H.,  Terrain  houiller  de  Commentry.     Saint-Etienne.     Livre  Premier,  Lithol- 
ogie  et  Stratigraphie,  1887. 

2  Stevenson,  J.  J.,  The  Coal  basin  of  Commentry  in  Central  France.     Ann.  N.  Y. 
Acad.  Sci.  XIX,  p.  161,  1910. 


130  THE   ORIGIN  OF   COAL 

the  17,000  years  postulated  by  Fayol  for  this  operation.  Stevenson 
believed  that  the  vegetation  of  this  coal  basin  accumulated  in  situ. 

Gresley1  regarded  coal  as  of  drift  origin  and  based  his  conclusions 
largely  upon  observations  in  the  Pittsburgh  seam  of  the  Appalachian 
province.  He  claimed  that  there  are  two  slate  partings  in  this  seam 
from  |  to  J  inch  thick  separated  by  3  to  4  inches  of  coal  and  occurring 
over  about  15,000  square  miles.  These  contain  no  Stigmaria  and  the 
underclay  of  this  seam  over  large  areas  is  a  calcareous  mud  without 
Stigmaria. 

One  of  the  strongest  supporters  of  the  in  situ  theory  was  Potonie.2 
He  describes  a  core  750  meters  long  from  the  upper  Silesian  coal 
measures  in  which  there  are  at  least  27  beds  of  coal  each  with  an  un- 
derclay carrying  Stigmaria.  He  also  describes  a  fossil  swamp  in  the 
Miocene  formations  near  Senftenberg  which  has  given  rise  to  .brown 
coal  and  in  which  several  generations  of  forests  have  grown  and  left 
their  stumps  rooted  in  the  vegetal  matter.  His  valuable  observations 
on  modern  fresh-water  swamps,  such  as  those  in  Sumatra,  have  also 
helped  a  great  deal  in  clarifying  our  ideas  on  ancient  peat-producing 
swamps.  He  has  suggested  the  following  terms  for  organic  deposits3 : 
Kaustobioliths,  or  combustible  rocks  of  organic  origin,  which  are 
divided  into  Sapropelic  deposits  or  those  composed  of  animals  and 
aquatic  plants  such  as  cannel  coal  and  oil  shales;  and  humus  deposits 
which  include  all  ordinary  coals. 

In  reviewing  the  literature  on  the  subject  of  the  accumulation  of 
peat  it  is  found  that  the  majority  of  writers  favor  the  autochthonous 
or  in  situ  theory,  but  there  are  many  scientists  of  note  who  favor  the 
opposite  view.  Among  living  geologists  the  former  theory  is  most 
generally  accepted  and  it  is  particularly  well  demonstrated  in  the 
discussions  of  White4  and  his  colleagues,  although  White  accepts  the 
drift  theory  for  some  lesser  deposits.  On  the  other  hand,  Jeffrey,5 

1  Gresley,  W.  S.,  The  slate  binders  of  the  Pittsburgh  coal  bed,  Amer.  Geologist,  XIV, 
p.  356,  1894. 

2  Potoni6,  H.,  Ueber  Autochthonie  von  Carbonkohlen-Flotzen  und  des  Senftenberger 
Braunkohlen-Flotzes  Jarb.  d.  k.  Preuss.  Geolog.  Landesanstalt,  1895. 

3  Potonie,  H.,  Die  Enstehung  der  Steinkohle  und  der.Kaustobiolithe  iiberhaupt  wie 
des  Torfes  der  Braunkohle  des  Petroleums  u.  s.  w.  5th  ed.,  1910. 

4  White,  David,  and  Thiessen,  R.,  The  origin  of  coal.     U.  S.  Bureau  of  Mines,  Bull. 
38,  1913- 

6  Jeffrey,  E.  C,  The  mode  of  origin  of  coal.  Jour,  of  Geol.,  Vol.  XXIII,  1915,  p.  218. 
Also,  Petrified  coals  and  their  bearing  on  the  problem  of  the  origin  of  coals.  Proc.  Nat. 
Acad.  Sciences,  Vol.  Ill,  p.  206,  1917. 


THE   DEVELOPMENT   OF   PEAT 


the  paleobotanist  as  a  result  of  his  extensive  microscopic  studies 
is  a  strong  advocate  of  the  drift  theory,  perhaps  in  a  somewhat  modi- 
fied form.  His  conclusions  are  based  very  largely  on  the  abundance 
of  spore  remains,  thus  suggesting  accumulation  of  the  vegetal  matter 
in  open  water,  as  in  cannel  coal. 

The  writer  believes  that  the  majority  of  our  coal  seams  are  un- 
doubtedly autochthonous  in  origin  as  most  of  the  evidence  supports 
this  theory.  Owing,  however,  to  the  strong  arguments  advanced 
and  supported  by  both  schools  on  this  subject  he  agrees  that  some  of 
the  less  extensive  deposits  have  been  allocthonous,  especially  the 
lens-shaped  seams  of  limited  extent  occurring  in  lacustrine  and  estuar- 
ine  formations  of  the  delta  type. 

Discussion  of  the  Theories  of  the  Origin  of  Coal 

(1)  The  development  of  peat  in  bogs,  marshes,  and  swamps.  Peat- 
bogs. —  At  the  present  day  a  vast  amount  of  peat  is  being  formed  in 
small  lakes  and  bogs,  particularly  in  the  cooler,  wet  climates  and  in 


; 


FIG.  18.  —  Diagram  illustrating  the  formation  of  peat  in  a  bog  and  the 
extension  of  the  larger  trees  over  the  peat  deposit. 

the  regions  which  have  been  glaciated  and  where  drainage  is  there- 
fore poor.1  The  depth  of  the  peat  may  vary  from  a  few  inches  to 
50  feet  but  the  detached  areas  covered  by  it  are  comparatively  small 
and  while  a  peat-bog  may  serve  to  demonstrate  how  vegetal  matter 
accumulates  in  considerable  quantities  it  is  in  no  way  comparable  in 
extent  to  the  great  bodies  of  vegetation  which  must  have  given  rise 
to  our  important  coal  seams.  These  peat-bogs  generally  begin  with 
a  pond  or  a  small  lake  varying  from  a  few  hundred  feet  up  to  a  mile 
or  more  in  diameter.  The  development  of  the  peat  begins  with  the 
growth  and  partial  decay  of  a  fringe  of  plants  around  the  border  of 
1  Davis,  C.  A.,  The  origin  of  peat.  U.  S.  Bur.  of  Mines,  Bull.  38,  pp.  165-186,  1913. 


132  THE   ORIGIN  OF   COAL 

the  lake.  The  first  plants  to  develop  are  usually  the  pond  weeds  and 
water  lilies.  These  are  followed  by  the  bulrushes  and  beyond  them 
the  floating  algae  live  in  the  deeper  water  where  they  do  not  reach 
the  bottom.  As  this  vegetation  grows  and  dies,  season  after  season, 
a  deposit  of  peat  develops  along  the  shore  and  as  it  grows  higher  the 
plants  mentioned  gradually  shift  their  relative  position  farther  out 
from  the  shore  and  toward  the  center  of  the  lake  (Fig.  18).  In  the 
course  of  time  a  growth  of  sphagnum  or  "peat-moss,"  a  large  grayish- 
green  or  whitish  moss,  extends  outwards  over  the  peat  deposit  and 
this  is  followed  by  small  trees  of  several  species,  chiefly  the  conifers; 
including  the  tamarack  and  spruce.  As  the  peat  becomes  more  and 
more  firm,  larger  and  larger  trees  will  be  supported  and  deciduous 
trees  such  as  the  white  birch  may  partially  replace  the  conifers.  In 
time  the  lake  may  be  completely  filled  up  and  the  area  overgrown  by 
small  timber. 

As  the  peat  develops  several  zones  may  be  observed  in  the  deposit. 
A  very  dark,  heavy,  dense  peat  forms  at  the  bottom  and  lighter- 
colored,  more  fibrous  layers  occur  as  the  surface  is  approached.  Scat- 
tered through  these  layers  there  may  be  trunks  of  trees  more  or  less 
altered.  These  trees  grew  around  the  border  of  the  lake  and  were 
killed  at  times  of  high  water,  or  they  may  have  been  blown  down  or 
otherwise  killed  and  they  then  became  imbedded  in  the  peat.  In 
seasons  when  the  water  is  low  and  the  surface  of  the  bog  stands  above 
the  water-soaked  level  the  vegetation  may  suffer  considerably  more 
decomposition,  or  dry  rot,  than  in  other  seasons  and  all  but  the  more 
resistant  portions  of  the  material  will  be  destroyed.  This  may,  if 
carried  sufficiently  far,  give  rise  to  mineral  charcoal.  In  wet  seasons 
when  the  water  is  high,  a  much  smaller  degree  of  decomposition  occurs 
and  a  much  greater  proportion  of  the  vegetation  is  preserved  so  that 
alternate  bands  with  varying  composition  result. 

Marshes:  In  addition  to  the  peat  bogs  there  are  in  various  parts 
of  the  world  large  areas  without  trees,  where  peat  forms  a  shallow 
deposit  covering  a  water-soaked  land  surface,  but  where  standing 
water  is  not  usually  present  except  in  the  wet  seasons.  These  areas 
are  found  chiefly  in  the  frigid  and  terhperate  zone,  but  they  may  also 
be  found  in  the  tropics.  In  the  colder  regions  the  peat  consists  mostly 
of  sphagnum,  but  in  some  places  rushes  and  grasses  may  form  a  con- 
siderable part  of  the  plant  growth.  The  Arctic  tundra  is  one  type  of 


THE   DEVELOPMENT  OF   PEAT 


133 


such    deposit.     In    the    warmer    climates    cane-brakes    and    "tuie" 
marshes  represent  this  type  of  peat  development. 

Fresh-water  swamps:  Interesting  as  the  peat  bogs  and  marshes 
may  be  in  illustrating  various  ways  in  which  peat  may  develop,  they 
cannot  be  regarded  as  the  sources  of  the  peat  which  gave  rise  to  im- 


FIG.  19.  —  Cowhouse  Run,  Okefinokee  Swamp,  Ga. 
(Photo  by  Francis  Harper.) 

portant  deposits  of  coal.  There  is  sufficient  peat  in  the  temperate 
regions  of  the  world  today  to  form  large  amounts  of  coal,  if  it  were 
concentrated  into  coal  seams,  but  no  single  bog  or  marsh  known  would 
supply  sufficient  peat  to  make  a  large  coal  seam,  although  Geikie 
states  that  one-seventh  of  Ireland  is  covered  with  peat  bogs  and  in 
Allen  alone,  238,500  acres  are  covered  with  peat  to  an  average  depth 
of  25  feet. 

There  are,  however,  other  deposits  of  peat  forming  at  the  present 
day  in  both  temperate  and  tropical  regions,  which  much  more  nearly 


134 


THE   ORIGIN  OF  COAL 


represent  the  kind  of  accumulation  of  vegetation  which  gave  rise  to 
extensive  coal  seams.  These  deposits  are  forming  in  immense  fresh- 
water swamps  such  as  the  Dismal  Swamp  of  North  Carolina  and 
Virginia  and  the  Sumatra  swamp  in  the  East  Indies.  Large  swamps 
of  similar  character  are  believed  to  exist  in  tropical  Africa  and  South 
America.  From  descriptions  of  these  swamps  it  is  apparent  that  the 
idea  so  commonly  held  that  peat  can  scarcely  form  in  warm  climates 
and  that  modern  deposits  of  peat  are  practically  restricted  to  the 


FIG.  20. —  Scene  in  a  cypress  bay,  Okefinokee  Swamp,  Ga 
(Photo  by  Francis  Harper.) 

cooler  regions  of  the  earth  is  not  correct.  In  fact  there  are  deposits 
of  peat  in  these  swamps  much  more  nearly  approaching  large  coal 
seams  in  extent  than  anything  found  in  the  cooler  regions.  If  there 
be  an  abundant  rainfall  on  poorly  drained  land  and  a  type  of  vege- 
tation capable  of  very  rapid  growth,  the  wastage  of  peat  due  to  higher 


THE    DEVELOPMENT   OF   PEAT 


135 


temperature  may  be  offset  by  the  greater  rate  of  growth  in  tropical 
or  sub-tropical  climates. 

According  to  Shaler1  the  inundated  portion  of  the  Dismal  Swamp 
is  about  38  miles  north  and  south  by  25  miles  east  and  west.     The 


FIG.  21.  —  Map  of  the  Dismal  Swamp.  North  Carolina  and  Virginia,  showing 
the  relation  of  the  swamp  to  the  coastal  plain.      (After  Shaler,  U.  S.  Geol.  Survey.) 

swamp  which  was  apparently  extending  its  borders  before  man  began 
to  drain  and  cultivate  portions  of  it  is  now  considerably  smaller  than 

1  Shaler,  N.  S.,  Geology  of  the  Dismal  Swamp  District  of  Virginia  and  North  Carolina. 
U.  S.  Geol.  Survey,  Tenth  Ann.  Kept.,  Pt.  i,  pp.  313-339,  1888-9. 


136  THE   ORIGIN  OF  COAL 

it  was  originally.  Osbon  places  the  total  area  of  this  swamp  originally 
at  2200  square  miles  with  700  now  drained.1  It  lies  on  the  coastal 
plain  and  represents  the  largest  continuous  swamp  area  of  the  many 
scattered  over  this  plain  between  the  Appalachian  Mountains  and  the 
sea  (Fig.  21).  The  rocks  underlying  the  swamp  are  mostly  strati- 
fied marine  sands  with  some  lime  beds  probably  of  Pliocene  age.  The 
surface  is  slightly  rolling  or  billowy  but  the  differences  in  elevation 
are  small  and  on  the  whole  the  area  approaches  a  level  surface  from 
5  to  25  feet  above  the  sea.  The  geological  events  which  have  given 
rise  to  the  present  relief  are  outlined  by  Shaler  as  follows:  (i)  A 
subsidence  leading  to  the  formation  of  the  Pliocene  plateau.  (2) 
Elevation  permitting  erosion  of  the  plateau.  (3)  Subsidence  permit- 
ting deposition  of  non-fossiliferous  sands.  (4)  Elevation  permitting 
carving  of  surface.  (5)  Subsidence  and  formation  of  the  Nansemond 
escarpment.  (6)  Reelevation  and  development  of  valleys  of  streams 
to  present  depth.  (7)  Sinking  now  taking  place. 

From  this  description  it  is  seen  that  this  swamp  stands  near  the 
critical  level  in  much  the  same  way  as  the  swamps  of  the  coal  measures 
must  have  been  situated  and  that  a  slight  change  in  elevation  might 
produce  dry  land  or  a  transgression  of  the  sea.  There  are  areas  of 
open  water  in  this  swamp,  such  as  Lake  Drummond,  which  might 
represent  the  more  extensive  areas  of  open  water  in  the  coal  measure 
swamps  in  which  the  spores  collect  and  produce  canneloid,  thus 
giving  rise  to  lenses  of  cannel  coal.  This  lake  is  gradually  filling  up 
with  peat  by  the  encroachment  of  the  vegetation.  There  are  other 
areas  which  are  never  completely  submerged  and  which  are  compara- 
tively dry  during  the  greater  part  of  the  dry  seasons.  These  exposed 
areas  would  illustrate  those  on  which  mineral  charcoal  would  form 
because  of  more  extensive  rotting  resulting  from  exposure  (Fig.  22). 

The  vegetation  in  this  swamp  varies  with  the  amount  of  water 
present.  The  higher  levels  are  usually  occupied  by  pines  such  as  the 
common  southern  pine.  The  lower  levels  are  mainly  occupied  by 
three  species  of  trees,  the  Taxodium,  or  bald  cypress,  the  juniper, 
and  the  black  gum.  The  juniper  occurs  on  the  land  which  becomes 
fairly  well  dried  during  the  dry  season.  The  other  two  may  grow  in 
areas  continuously  covered  with  water  if  the  water  does  not  rise  too 

1  Osbon,  C.  C.,  Peat  in  the  Dismal  Swamp,  Virginia  and  North  Carolina.  U.  S. 
Geol.  Survey,  Bull.  yn-C,  1919. 


THE   DEVELOPMENT  OF  PEAT 


137 


high,  as  they  develop  knees,  or  arched  roots  to  aid  in  keeping  them- 
selves above  water. 

The  fallen  trees,  the  spores,  the  leaves,  and  other  plant  debris  are 
continually  falling  into  the  water  in  this  swamp  and  building  up  a 
layer  of  peat  which  has  been  estimated  at  i  to  20  feet  in  thickness. 
Osbon  has  estimated  that  1500  square  miles  are  covered  to  an  average 


FIG.  22. —  Lake  Drummond,  Dismal  Swamp. 
Geol.  Survey.) 


(Photo  by  Shaler,  U.  S. 


depth  of  7  feet  and  that  the  total  available  peat  in  this  swamp  is  about 
672,000,000  tons.  This  peat  if  turned  to  coal  would  be  sufficient  to 
form  a  seam  from  about  i  inch  to  20  inches  in  thickness  and  it  would 
have  many  of  the  characteristics  of  coal  seams  as  we  are  familiar  with 
them  today.  The  ash  content  is  quite  satisfactory.  If  the  sinking 
of  this  area  continued  very  slowly,  the  living  vegetation  would  be 
destroyed  and  opportunities  would  be  offered  for  the  collection  and 
preservation  of  a  large  amount  of  vegetation.  It  might  become 
buried  by  the  encroachment  of  the  sea  and  the  deposition  of  sediments 
over  the  vegetation.  Submerged  stumps  in  the  valley  of  the  Pamlico 
River,  in  this  area,  indicate  that  in  comparatively  recent  time,  geol- 


138  THE   ORIGIN  OF  COAL 

ogically  speaking,  submergence  has  occurred.  On  the  other  hand  a 
slight  uplift  of  the  land  surrounding  this  basin  might  cause  large 
quantities  of  mud,  sand,  or  gravel  to  be  washed  into  the  swamp  and 
form  partings  in  the  resulting  coal  when  a  new  swamp  formed  on  top 
of  this  rock. 

The  other  large  fresh-water  swamp  of  which  we  have  some  definite 
knowledge  is  one  on  the  island  of  Sumatra  described  by  Potonie.1 
It  is  said  to  cover  about  312  square  miles.  The  peat  deposit  reaches 
a  thickness  of  9  meters  or  nearly  30  feet  in  this  swamp  and  it  is  made 
up  of  a  mixture  of  logs  and  plant  debris  of  all  sorts.  There  is  a  stag- 
nant, tea-colored  blanket  of  fresh-water  over  the  peat,  which  makes 
an  efficient  preserving  fluid  for  the  materials  which  fall  into  it.  The 
ash  content  of  the  dried  peat  is  6.39  per  cent.  This  material  if  com- 
pressed into  bituminous  coal  should  produce  a  seam  nearly  3  feet 
thick,  as  the  lower  layers  of  peat  have  already  undergone  considerable 
change  and  they  are  dense  and  compact. 

That  many  swamps  and  forests  have  become  buried  beneath  mar- 
ine and  fresh- water  deposits  is  well  demonstrated  by  Stevenson2  in 
his  article  on  " Buried  Forests."  An  interesting  example  is  also 
mentioned  by  Mietzsch3  who  says  that  off  Rotterdam  two  bogs, 
5  meters  and  6  meters  thick,  are  separated  by  a  bed  of  clay  4  meters 
in  thickness.  Some  of  the  trees  are  still  standing  and  they  are  of 
types  which  inhabited  the  adjacent  lands  centuries  ago.  Another 
of  greater  antiquity  was  described  by  Potonie  from  the  Miocene  and 
previously  mentioned  in  this  chapter.  In  these  illustrations  we  seem 
to  have  abundant  evidence  of  the  efficacy  of  fresh-water  swamps  in 
producing  coal  deposits  under  proper  climatic  and  topographic  con- 
ditions. 

Mangrove  swamps:  There  are  also  certain  salt  and  brackish  water 
swamps,  which  occur  along  the  sea  coasts  and  in  which  the  trees  are 
mostly  mangroves.  They  are  known  as  mangrove  swamps.  These 
are  found  in  the  tropical  or  semi-tropical  regions  and  some  of  them 
are  of  considerable  extent.  They  may  be  seen  in  northern  New 
Zealand,  Ceylon,  Cuba,  Florida,  and  many  other  countries  (Fig.  26). 

1  Potonie,  H.,  Die  Entstehung  der  Steinkohle  und  der  Kaustobiolithe  iiberhaupt, 
5th  ed.,  pp.  152-160,  1910. 

2  Stevenson,  J.  J.,  The  formation  of  coal  beds,  Pt.  II,  Proc.  Amer.  Phil.  Soc.,  Vol.  50, 
p.  626,  1911. 

3  Loc.  cit. 


DRIFTED   VEGETATION  AND   DELTA   DEPOSITS 


139 


The  long  stilt-like  roots  raise  the  trunk  above  the  water  and  among 
these  roots  the  vegetal  debris  collects.  They  sometimes  extend  a 
short  distance  from  the  shore  where  the  water  is  shallow  and  while 
considerable  peat  forms  in  such  a  swamp,  so  far  as  the  writer's  ob- 
servations go,  there  is  always  a  large  amount  of  sand  mixed  with  the 
peat  owing  to  the  tidal  currents  and  storm-waves  which  wash  it  into 
the  swamp.  This  type  of  swamp  never  seemed  very  favorable  for 


FIG.  23.  —  Portion  of  Dismal  Swamp  in  which  peat  is  covered  with  water.      (Photo  by 
Shaler,  U.  S.  Geol.  Survey.) 

the  formation  of  extensive  bodies  of  peat.  These  trees  may,  however, 
grow  farther  back  from  the  sea  and  even  in  fresh-water  swamps  where 
conditions  are  more  favorable  to  the  formation  of  purer  peat  deposits. 
(2)  Drifted  vegetation  and  delta  deposits.  —  The  drift  theory  for 
the  collection  of  vegetation  giving  rise  to  coal  deposits  has  many  sup- 
porters who  naturally  invoke  processes  now  operative  on  the  earth's 
surface  to  substantiate  their  arguments.  They  can  point  to  a  few 
cases  where  coal  is  being  formed  or  has  been  formed  in  undoubted 
delta  deposits  in  comparatively  recent  time  considered  from  the 


140  THE  ORIGIN  OF  COAL 

geological  standpoint.  In  an  article  describing  briefly  the  artesian 
wells  at  Venice,  Italy,  Degousee1  mentions  lignite  beds  which  were 
pierced  in  drilling  for  water.  He  states  that  the  sea  is  very  shallow 
in  the  Gulf  of  Venice  for  a  long  distance  from  the  shore  At  a  depth 
of  60  to  70  meters  and  above  the  real  artesian  bed  ascending  water  is 
struck  which  is  so  charged  with  hydrogen  carbide  that  the  water  is 
intermittently  thrown  above  the  surface  with  great  violence.  This 
gas  is  said  to  burn  well  but  nothing  is  recorded  regarding  its  relation 
to  the  lignite  beds,  fn  all  the  wells  bored  several  beds  of  lignite  in 
sand  and  clay  were  passed  through.  Unfortunately  we  have  no  de- 
tailed data  concerning  the  thickness  or  number  of  these  seams.  There 
were  in  the  lignite  fragments  of  wood  sufficiently  preserved  to  be 
identified. 

Reference  is  frequently  made  in  literature  to  the  enormous  amount 
of  timber  floating  down  the  Mississippi  River  and  the  rafts  of  drift- 
wood, several  miles  in  length,  which  years  ago  blocked  the  channel 
of  the  stream.  Conditions  as  they  are  at  present,  in  the  cleared  and 
cultivated  valley  of  that  river,  make,  however,  a  poor  parallel  to  the 
conditions  prevailing  when  the  country  was  covered  with  virgin  forest, 
as  a  vastly  greater  proportion  of  mineral  matter  is  being  carried  than 
would  have  been  carried  then.  A  closer  parallel  to  the  conditions 
prevailing  when  coal  was  being  formed  may  possibly  be  seen  in  some 
of  the  rivers  in  northern  Canada  where  many  streams  flow  through 
regions  covered  with  virgin  forests  and  peat  bogs.  One  is  impressed, 
for  example,  by  the  vast  quantities  of  timber  which  descend  the 
streams  to  James  Bay  every  spring  (Fig.  27).  Owing,  however,  to 
the  great  variation  in  size  of  the  fragments  and  the  difference  in  the 
rate  at  which  they  become  water-logged  and  sink,  or  float  out  to  sea, 
there  seems  little  opportunity  for  this  material  to  collect  into  any 
extensive  bodies  of  peat  on  the  sea  bottom.  One  of  the  main  diffi- 
culties in  the  way  of  its  producing  coal  is  the  fact  that  when  most 
plant  debris  is  carried  in  flood  periods  there  is  always  more  than  the 
normal  quota  of  mineral  matter  taken  along. 

In  an  effort  to  obtain  definite  information  regarding  the  proportion 
of  plant  debris  carried  by  streams  and  thus  support  his  arguments 

1  Degousee,  M.  J.,  Note  sur  les  alluvions  formant  les  lagunes  venitiennes,  et  sur  les 
puits  artesiens  de  la  ville  de  Venise.  Bull,  de  la  Societe  Geologique  2  Serie,  Tome  8, 
pp.  481-4,  1850. 


DRIFTED   VEGETATION  AND   DELTA  DEPOSITS 


141 


for  the  drift  theory  for  the  basin  of  Commentry,  central  France, 
Fayol1  stretched  a  wire  screen  of  one  centimeter  mesh  across  a  stream 
known  as  the  Baune.  This  was  done  in  the  month  of  January  and 
it  collected  502  grams  in  2  minutes,  or  1.5  grams  for  each  cubic  meter 
of  water  passed  through.  He  also  made  certain  laboratory  exper- 
iments in  a  small  body  of  water  to  determine  the  action  of  vegetal 
matter  in  sinking  to  the  bottom  and  of  mixing,  or  separating  itself 


FIG.  24.  —  Timber  undergoing  partial  decay  in  the  Dismal  Swamp.     (Photo  by  Shaler, 

U.  S.  Geol.  Survey.) 

from  the  sediment  which  was  carried  into  the  body  of  standing  water 
with  the  plant  materials.  He  found  that  the  roots  were  among  the 
first  materials  to  sink.  Many  stems  remained  in  an  upright  or  in- 
clined position  on  the  bottom  and  the  plant  debris  formed  deposits 
varying  from  practically  pure  vegetal  matter  to  those  highly  mixed 
with  mineral  matter. 
According  to  this  writer,  the  basin  at  Commentry,  in  Carboniferous 

1  Fayol,  Henri.     Terraine  houiller  de  Commentry,  Livre  Premier,  fitudes  sur  le  terrain 
houiller  de  Commentry,  p.  397,  1887. 


142 


THE  ORIGIN  OF  COAL 


time  was  occupied  by  a  fresh-water  lake  surrounded  by  high  lands. 
Streams  entered  the  lake  with  sufficient  gradient  to  move  large 
boulders,  some  of  granite  in  the  conglomerate  underlying  the  coal 
reaching  a  cubic  meter  in  volume  and  suggesting  for  them  a  glacial 
origin.  As  a  parting  in  the  famous  Grande  Couche,  a  seam  reaching 
a  maximum  thickness  of  20  meters,  there  are  8  meters  of  conglomerate 
with  some  boulders  half  a  meter  in  diameter.  Another  peculiar 


9 

=5*44- 


FIG.  25.  — •  Destruction  of  trees  by  high  water  in  the  Dismal  Swamp.      (Photo  by 
Shaler,  U.  S.  Geol.  Survey.) 

feature  of  these  coal  deposits  is  the  presence  in  the  conglomerates  of 
the  Coal  Measures  of  pebbles  of  coal  and  abundant  grains  of  coal 
in  the  sandstones  showing  that  older  coal  beds  had  been  broken  up 
by  erosion. 

Some  of  the  other  evidences  of  the  drift  origin  of  the  coal  at  Com- 
mentry  are  trees  with  their  trunks  in  an  inverted  position,  and  the 
presence  of  abundant  fossil  fish  in  the  associated  rocks.  The  occur- 
rence of  inverted  tree  trunks  cannot,  however,  always  be  regarded  as 
conclusive  evidence  of  drift  origin  because  one  may  often  see  trees  in 
a  swamp  broken  off  by  the  wind  and  embedded,  head  down,  in  the 


DRIFTED   VEGETATION   AND   DELTA   DEPOSITS  143 

peat.  Their  chances  for  preservation  are,  however,  not  great  unless 
covered  with  clay  or  sand,  since  most  of  them  project  above  the  water- 
level.  The  presence  of  upright  trunks  and  stumps  on  the  other  hand 
cannot  be  regarded  in  many  cases  as  definite  evidence  of  growth  in 
place  because  a  stump  floating  into  a  body  of  water  will  most  likely 
settle  to  the  bottom  in  an  upright  position,  owing  to  the  weight  of  the 
roots  if  they  be  present,  or  the  greater  weight  of  the  big  end  of  the 
trunk,  when  water-logged,  if  roots  be  absent.  There  are  stumps 
in  the  Coal  Measures  at  St.  fitienne,  France,  with  a  number  of  roots 
penetrating  the  underlying  rocks  but  it  is  impossible  to  determine 
whether  the  stumps  are  in  place  or  whether  they  floated  to  their 
present  position  and  became  buried  by  sediment  (Fig.  28) .  If,  how- 
ever, the  unbroken  rootlets  are  found  in  their  proper  position  and 
roots  are  found  piercing  fragments  of  buried  wood  this  would  be 
regarded  as  proof  of  their  growth  in  situ.  Such  conditions  are  found 
in  many  of  the  great  coal  fields. 

Some  writers  attach  importance  to  the  relative  number  of  upright 
stumps  and  trunks  in  the  coal  and  in  the  adjacent  conglomerates, 
sandstones,  and  shales.  This  circumstance  cannot  carry  any  par- 
ticular weight  in  the  argument  because  it  is  evident  that  these  rocks 
are  capable  of  supporting  the  trunks  in  this  upright  position  and 
they  were  buried  quickly;  whereas  the  soft,  yielding  peat  would 
permit  them  to  be  easily  crushed  down  flat  by  the  superincumbent 
load  of  rock  or  vegetal  matter.  Fayol  observed  that  in  the  Commentry 
basin  99.5  per  cent  of  the  stems  were  flat  in  the  coal  and  0.5  per  cent 
vertical  or  inclined.  In  the  sandstones  70  per  cent  were  flat  and  in 
the  conglomerates  60  per  cent. 

The  fact  that  so  much  better  plant  remains  are  found  in  the  shales 
and  "  coal  balls"  than  in  the  coal  itself  is  due  to  the  soft,  pliable  peat, 
which  gave  rise  to  the  coal,  squeezing  and  creeping  under  the  weight 
of  the  overlying  rocks  and  to  partial  decomposition  of  the  vegetal 
matter  because  of  longer  exposure  destroying  original  structures. 
In  many  cases  the  tree  will  rot  out  in  the  sandstone  or  shale  leaving 
perhaps  traces  of  the  bark  and  this  space  becomes  filled  later  by  sand 
or  clay  which  is  squeezed  into  it,  thus  giving  a  stone-cast  of  the  tree. 
The  rock  in  these  casts  often  differs  from  the  rock  surrounding 
them  because  it  has  been  squeezed  up  from  a  lower  stratum 
or  down  from  a  higher  stratum  than  the  one  holding  the  cast.  In 


144 


THE  ORIGIN  OF  COAL 


some  of  these  casts,  mineral  matter  from  solution  may  be  deposited 
where  the  wood  has  disappeared,  giving  more  iron  oxide,  calcium  car- 
bonate or  similar  mineral  than  is  found  in  the  surrounding  rock. 

The  sequence  of  conglomerate,  sandstone,  shale,  and  coal  beds  in 
varying  succession  argues  strongly  for  the  drift  theory  as  it  would 
appear  that  in  so  many  cases  there  was  almost  complete  assortment 
of  sediments  on  the  basis  of  specific  gravity  and  rate  of  settling. 
Further,  the  accumulation  of  vegetation  to  such  a  tremendous  depth 


iii 


FIG.  26.  —  Mangrove  swamp  creeping  out  over  the  sea  on  coast  of  New  Zealand. 
(Photo  by  E.  S.  Moore.) 

as  that  necessary  to  produce  50  or  60  feet  of  anthracite  might  seem  to 
some  most  easily  accounted  for  by  supposing  that  the  material  was 
transported  and  dumped  into  a  body  of  water  because  there  would 
be  little  opportunity  for  trees  growing  in  this  mass  to  root  in  anything 
but  peat.  It  has  been  shown,  however,  that  many  of  the  larger  trees 
which  occupied  the  swamps  were  specially  equipped  with  roots 
adapted  to  an  existence  near  the  surface  of  wet  peat  deposits  and  they 
were  no  doubt  supported  by  the  extensive  matting  together  and  inter- 
locking of  the  roots  of  the  forest  trees.  It  is  known  that  trees  of 
considerable  size  can  subsist  at  the  present  day  on  thick  deposits  of 
peat  and  it  seems  much  easier  to  explain  the  accumulation  of  such 
great  masses  of  peat,  so  free  from  mineral  matter  and  requiring  such 


DRIFTED   VEGETATION  AND   DELTA  DEPOSITS  145 

long  periods  to  form,  in  a  swamp  free  from  sediment  than  in  open 
water  where  every  season  large  quantities  of  mud  or  silt  are  likely  to 
be  carried  and  spread  over  it  during  floods. 

The  Sargasso  Sea:1  One  other  phase  of  the  drift  theory  may  be 
mentioned.  It  has  been  suggested  that  the  great  mass  of  plankton 
floating  on  the  ocean  might  segregate  in  the  eddies  in  the  ocean  cur- 
rents and,  sinking  to  the  bottom,  build  up  peat  deposits  which  would 
be  well  preserved.  This  mass  would  be  made  up  of  great  quantities 


FIG.  27.  —  Drifted  timber  along  the  Metagami  River,  James  Bay  basin,  Canada. 

(Photo  by  E.  S.  Moore.) 

of  very  small,  low  types  of  floating  plants  associated  with  sea-weed 
and  other  forms  of  plant  life  which  would  be  carried  about  on  the 
ocean  surface.  While  it  is  true  that  some  material  is  collecting  in 
this  way  at  the  present  time  anyone  familiar  with  ocean  travel  knows 
that  coal  beds  were  never  formed  in  this  way  because  there  is  not 
sufficient  material  being  deposited.  Deep-sea  dredgings  have  failed 
to  show  any  accumulation  of  plant  material  worth  mentioning.  Other 
convincing  evidence  opposing  this  theory  is  the  presence  of  coarse 
littoral  sediments  so  frequently  interbedded  with  the  coal  seams,  in- 
dicating that  these  sediments  are  shallow  water  or  land  formations 
and  not  deep-sea  deposits. 

1  Mohr,  F.,  Geschichte  der  Erde,  1886. 


146  THE  ORIGIN  OF  COAL 

Rate  at  which  Peat  Accumulates 

The  rate  at  which  peat  forms  in  any  given  region  will  depend  upon 
the  rate  of  growth  and  proportional  rate  of  decay.  The  nature  of 
the  vegetation  will  have  a  great  influence  on  the  rate  of  growth  as 
some  trees  grow  so  much  faster  than  others  on  an  area  partially  or 
entirely  covered  with  water,  the  condition  essential  for  the  preser- 
vation of  the  vegetation  after  it  is  grown.  Coarse  vegetation  will 
naturally  build  faster  than  fine  material  but  there  are  certain  types 
of  the  finer  plant  debris  which  build  at  a  fairly  rapid  rate  owing  to  the 
fact  that  the  proportional  shrinkage  is  not  so  great  as  in  the  coarse 
debris  and  the  material  is  being  supplied  to  the  bog  every  year.  If 
we  consider  for  example  the  spores  of  plants  which  fall  every  spring 
and  float  about  in  the  open  bodies  of  water  until  they  sink  we  will 
find  that  a  large  amount  of  this  material  collects  every  year  and  goes 
to  build  up  canneloid,  which  later  forms  cannel  coal.  The  writer  has 
seen,  while  traveling  in  the  late  spring  through  the  northern  woods 
of  this  continent,  such  quantities  of  spores  and  pollen  grains  from  the 
birch,  poplar,  and  related  trees  floating  on  the  water  of  the  small  lakes 
and  ponds  that  it  was  impossible  to  obtain  water  fit  to  drink.  There 
are  often  so  many  of  these  green  globules  in  the  water  that  in  places 
it  becomes  thick  with  them.  They  collect  in  bands  and  little  ridges 
along  the  shore  where  washed  up  by  the  waves.  It  can  be  easily  under- 
stood how  vast  quantities  of  these  spores  collecting  in  patches  of 
open  water  in  large  swamps  might  produce  lenses  of  cannel  with  the 
other  coal.  Modern  microscopic  investigations  of  coal  tend  to  show 
that  spores  are  very  widely  distributed  through  all  coal  and  that  owing 
to  their  resistance  to  decay  they  form  a  prominent  constituent  of  the 
coal.  Another  constituent  which  resists  decay  and  is  prominent 
in  many  coals,  especially  those  formed  chiefly  from  coniferous  trees, 
is  resin.  This  has  been  observed  in  considerable  proportions  in  micro- 
scopic studies. 

The  soil  will  have  some  influence  but  after  a  thick  layer  of  peat 
has  developed  the  plants  gather  most  of  their  sustenance  from  the 
air  and  water.  It  seems  probable  that  the  feldspathic  rocks  ob- 
served as  so  common  in  coal  measures  in  various  countries  of  the  world 
may  have  furnished  more  than  the  average  amount  of  potash  to  the 
vegetation,  which  was  able  to  root  in  the  soils  of  those  days,  and  thus 
produced  conditions  favorable  for  growth. 


RATE  AT  WHICH  PEAT  ACCUMULATES  147 

The  climate  plays  a  large  role  in  the  deposition  of  peat  because  a 
wet,  uniform  climate  will  produce  much  more  vegetation  in  a  given 
time,  other  things  being  equal,  than  a  climate  where  growth  and  pres- 
ervation are  limited  to  certain  seasons  of  the  year.  The  rate  of  de- 
cay in  a  warm  climate  will  be  greater  but  this  is  largely  offset  by  a 
good  water  blanket  for  the  fallen  plants.  The  latter  is  possible  only 
if  the  climate  be  uniformly  wet  throughout  the  year.  If  there  be 
long,  alternately  wet  and  dry  seasons,  there  will  be  little  peat  formed, 
unless  the  climate  be  cool,  no  matter  how  much  rain  falls. 

There  is  no  satisfactory  way  of  computing  the  rate  at  which  peat 
accumulated  in  the  coal-forming  periods.  We  can  only  judge  the 
rate  approximately  by  considering  the  amount  of  peat  which  forms 
at  the  present  day  in  a  given  time  and  it  is  only  in  a  few  areas  that 
definite  information  can  be  obtained  regarding  the  rate  of  formation 
of  modern  peat  deposits.  Where  a  forest  is  cut  away  or  where  peat 
grows  over  a  road  or  other  cultural  feature  whose  age  is  known, 
quite  accurate  data  may  be  obtained  regarding  its  growth.  Lesquer- 
eaux  considers  that  in  the  Jura  of  Switzerland,  peat  has  formed  to  a 
depth  of  1 8  to  20  inches  on  an  area  which  has  been  cut  over  within 
50  years.  Geikie1  gives  quite  a  number  of  cases  where  the  rate  of 
growth  is  well  established.  In  the  valley  of  the  Somme,  3  feet  of 
peat  has  developed  in  30  to  40  years,  and  on  a  moor  in  Hanover  4 
to  6  feet  has  grown  in  about  30  years.  Near  Lake  Constance  a  layer 
3  to  4  feet  thick  has  required  only  24  years  while  among  the  Danish 
mosses  10  feet  required  250  to  300  years  for  its  deposition. 

In  summing  up  the  data  concerning  the  rate  of  growth  of  peat 
Ashley2  states  that  under  the  most  favorable  conditions  i  foot  may 
form  in  5  years,  and  that  i  foot  in  10  years  is  a  fair  average  maximum. 
In  the  larger  and  deeper  basins  the  rate  is  slower  and  in  any  case  the 
newly  formed  peat  soon  contracts  to  only  a  fraction  of  its  original 
bulk.  Lesquereaux  considers  that  a  foot  of  peat  at  the  surface 
shrinks  to  f  foot  at  depth  in  the  bog.  By  taking  into  account  the 
specific  gravity  of  the  peat  at  the  surface  and  at  depth,  it  is  possible 
to  arrive  at  an  approximate  figure  for  the  amount  of  old  peat  formed 
from  the  surface  layer.  It  is  generally  agreed  that  approximately 

1  Geikie,  A.,  Text-book  of  geology,  2nd  ed.,  p.  443,  1885. 

2  Ashley,  G.  H.,  The  maximum  rate  of  the  deposition  of  coal.    Econ.  Geol.  Vol.  2, 
PP-  34-47,  1907- 


148  THE  ORIGIN  OF  COAL 

i  foot  per  century  is  a  fair  average  rate  for  the  development  of  old 
compressed  peat. 

The  Amount  of  Coal  Derived  from  a  Given  Amount  of  Peat 

Having  considered  the  rate  at  which  peat  forms  we  may  take  up 
the  question  of  the  approximate  rate  of  the  formation  of  coal.  No 
definite  figures  can  be  obtained  on  this  subject  but  a  number  of  val- 
uable observations  have  been  made.  Renault1  has  decided  after  ob- 


FIG.  28.  —  Upright  trunk  in  Coal  Measures  at  St.  Etienne,  France.     Broken  at  base. 
(Photo  by  E.  S.  Moore.) 

serving  carefully  the  shrinkage  of  stems  of  trees  in  passing  from  wood 
to  coal  that  the  loss  is  from  eleven-twelfths  to  twenty-nine-thirtieths 
of  the  original.  This  is  for  the  change  to  bituminous  coal  of  the 
Commentry  basin  in  France.  Ashley2  from  calculations  made  on 
the  relative  specific  gravity,  and  on  the  loss  of  moisture  and  other 
constituents,  concludes  that  3  feet  of  old  peat  would  form  i  foot  of 
bituminous  coal  such  as  that  in  the  Pittsburgh  seam,  and,  as  a  rule, 
about  20  feet  of  vegetal  matter  will  form  i  foot  of  coal.  In  deducing 
his  figures  Ashley  has  also  used  other  interesting  examples  such  as  the 
shrinkage  in  the  vegetal  matter  which  formerly  filled  a  small,  deep 
basin  and  now  forms  a  thin  lens-shaped  layer  of  coal  on  the  bot- 

1  Renault,  B.,  Sur  quelques  microorganisms  des  combustibles  fossiles,  Bull,  de  la  Soc. 
de  1'industrie  min^rale,  3me  serie  Tome  13-14,  1899-190x5. 

2  Ashley.    Loc.  cit.,  p.  42. 


THE   AMOUNT  OF   COAL   DERIVED   FROM   PEAT  149 

torn  of  the  basin.  He  cites  another  case  where  two  basins  were 
connected  over  a  low  ridge  and,  considering  that  the  basins  were 
filled  to  a  given  level  so  that  the  peat  could  connect  over  the  ridge, 
an  approximation  may  be  reached  regarding  the  relative  amount  of 
coal  formed  on  the  ridge  and  in  the  basins  from  a  mass  of  peat  reach- 
ing a  given  level. 

If  a  foot  of  old,  compact  peat  forms  in  a  century  and  it  requires 
3  feet  of  this  peat  to  form  a  foot  of  bituminous  coal  it  will  require 
three  centuries  to  form  a  foot  of  coal  and  three  thousand  years  to 
form  a  seam  10  feet  thick. 

Various  attempts  have  been  made  to  express  the  change  from  wood 
to  coal  by  chemical  formulae  but  they  are  "unsatisfactory  because  the 
formula  given  for  cellulose  will  not  represent  the  chemical  composition 
of  all  the  material  entering  peat,  and  it  is  difficult  to  write  a  chemical 
formula  properly  expressing  the  composition  of  a  coal  seam.  There 
is  almost  no  end  to  the  formulae  which  might  be  written.  Renault1 
gives  the  following  to  illustrate  the  change  from  wood  of  Cordaites 
to  homogeneous  coal: 

(C6H1005)4  =  C9H60    +    7CH4    +    8C02    +    3H2O 

Cellulose          Bituminous      Marsh  gas    Carbon  dioxide       Water 
coal 

Parr's  formulae2  for  lignite  and  bituminous  coal  are: 

(1)  5(C6H1005)  =  C20H2204  +  3CH4  +  8H2O  +  6CO2  +  CO 

Cellulose  Lignite        Marsh  gas      Water        Carbon     Carbon 

dioxide    monoxide 

(2)  6(C6H1005)  =  C22H200  +  5CH4  +  ioH2O  +  8CO2  +  CO 

Bituminous 
coal 

These  formulae  are  valuable  in  showing  the  relative  proportions 
of  the  various  constituents  of  the  wood  which  are  supposed  by  these 
investigators  to  be  lost  but  they  cannot  be  taken  too  literally  as 
representing  the  changes  which  have  taken  place. 

1  Renault,  Loc.  cit.,  p.  299 

2  Parr,  S.  W.,  Illinois  Geol.  Survey,  Bull.  3,  1906. 


THE  ORIGIN  OF  COAL 


The  Topographic  Conditions  Prevailing  During  Coal- 
forming  Periods 

On  examining  the  topography  of  any  of  the  continents  as  they 
existed  prior  to  and  during  the  deposition  of  the  vegetation  giving  rise 
to  the  great  coal  deposits,  it  is  found  that  extensive,  low  swampy 
areas  were  very  characteristic.  The  coal-forming  periods  invariably 
followed  periods  when  shallow,  continental  seas,  which  were  gradually 
filling:  up,  had  spread  over  considerable  areas  of  the  continent.  These 


FIG.  29.  —  Section  at  Treve,  France  showing  numerous  stumps  in  Coal  Measures. 

(After  Grand  'Eury.) 

seas  gradually  retreated  leaving  great  expanses  of  low  land,  poorly 
drained  and  ideal  for  the  development  of  swamps  on  a  large  scale. 
The  conditions  must  have  been  closely  parallel  to  those  now  found 
on  our  great  coastal  plains  along  the  Atlantic  Ocean  and  the  Gulf 
of  Mexico.  In  the  eastern  part  of  North  America  the  deposition  had 
been  predominantly  marine  previous  to  the  Carboniferous  period. 
During  this  period  the  land  over  most  of  this  part  of  the  continent 
began  to  emerge  finally  from  the  sea,  never  again  to  become  an  area 
of  extensive  marine  deposition,  although  the  western  portion  of  the 
present  continent  continued  to  be  covered  with  the  sea.  With  the 
emergence  of  this  great  area  there  was  a  differential  rise  of  the  area 
bordering  on  the  Atlantic  and  lying  between  the  Atlantic  as  it  then 
existed,  and  a  long  northeast-southwest  sound  on  its  westward 
side,  known  as  the  Appalachian  trough.  This  trough  was  being  filled 
with  sediments  from  the  land  masses  forming  Appalachia  on  the  east, 


TOPOGRAPHIC   CONDITIONS   DURING  COAL-FORMING  PERIODS     151 

the  pre-Cambrian  areas  to  the  north,  and  the  Cincinnati  arch  to  the 
northwest.  These  land  masses  continued  to  be  the  source  of  clastic 
sediments,  for  the  area  occupying  the  old  Appalachian  trough  became 
practically  filled  with  sediments  at  the  beginning  of  the  Carboniferous 
period,  presenting  the  aspect  of  an  extensive  coastal  plain.  This 
great  flat  area  was  subject  to  very  gentle  warpings,  probably  the 
forerunners  of  the  larger  buckling  movements  which  later  produced 
the  Appalachian  Mountains  at  the  close  of  the  coal-forming  period. 
This  area  was  so  near  sea  level  that  a  slight  rise  brought  it  into  the 
condition  of  dry  land  or  a  small  subsidence  put  it  below  the  ocean 
just  as  minor  changes  cause  the  Atlantic  coastal  plain  of  the  present 
day  to  rise  above  or  fall  below  the  sea. 

In  the  larger  of  the  depressions  formed  by  warping  of  the  strata 
the  swamps  giving  rise  to  the  more  extensive  coal  seams  such,  for 
example,  as  the  Pittsburgh  seam  originated.  In  many  of  the  depres- 
sions slow  subsidence  was  constantly  going  on  as  these  basins  were 
being  filled  up  with  vegetal  matter  and  sediment  but  it  seems  probable 
that  the  conditions  can  be  best  accounted  for  by  frequent  small 
elevations  of  the  surrounding  land  and  consequent  relative  sinking 
of  the  low  areas.  In  some  cases  the  conditions  even  permitted  en- 
croachment of  the  sea,  the  destruction  of  forests,  and  the  deposition 
of  limestones  and  other  marine  deposits  over  the  accumulated  vegetal 
matter.  Much  of  the  sediment  found  associated  with  coal  seams 
consists  of  feldspathic  sands  indicating  incomplete  decomposition,  as 
if  the  materials  composing  the  rock  had  been  swept  off  a  land  surface 
where  rocks  were  disintegrating.  These  products  of  disintegration 
might  have  been  carried  off  to  the  basins  owing  to  change  of  climate, 
or  elevation  of  the  land  on  which  they  were  lying,  causing  greater 
activity  of  water.  These  materials  could  be  derived  from  the  dis- 
integration of  granitic  rocks  and  they  could  be  rapidly  transported 
to  an  area  of  deposition  without  being  completely  sorted  or  water- 
worn  if  streams  became  very  active  owing  to  increase  in  velocity  due 
to  increase  in  gradient  or  volume  of  water. 

The  general  absence  of  extensive  erosional  features  in  the  measures 
during  Carboniferous  time  indicates  that  there  was  a  general  sub- 
sidence in  progress  and  that  the  swampy  areas  were  seldom  raised 
sufficiently  above  the  sea  to  permit  much  erosion  of  the  formations 
carrying  the  coal.  They  were  areas  of  deposition  rather  than  erosion. 


152 


THE  ORIGIN  OF   COAL 


The  red  beds  of  the  later  Permian  indicate  a  drier  climate  than  that 
which  had  prevailed  during  the  Carboniferous  and  the  coal-forming 
process  had  practically  ceased  when  the  larger  movements  producing 
the  Appalachian  Mountains  occurred. 

An  examination  of  the  conditions  in  the  western  part  of  the  con- 
tinent at  a  later  period  shows  that  the  conditions  found  in  the  east 
during  the  Carboniferous,  (Mississippian  and  Pennsylvanian)  were 


FIG.  30.  —  Upright  trunk  in  Coal  Measures  showing  roots  descending  into  rock  to 
right  of  the  hammer.    (Photo  by  E.  S.  Moore.) 

practically  duplicated  in  the  west  during  the  Jurassic  and  Cretaceous 
periods.  During  the  former  period  a  large  shallow  sea  extended  over 
the  region  now  occupied  by  the  Cretaceous  and  Tertiary  coal  deposits. 
This  sea  gradually  withdrew  from  the  land  and  conditions  became 
favorable  for  extensive  swamp  development.  The  coal-forming  proc- 
esses ended  with  the  elevation  of  the  Rocky  Mountains  as  it  did  in  the 
east  with  the  rise  of  the  Appalachians.  An  examination  of  other 
continents  will  reveal  a  similar  close  relation  between  the  topographic 
conditions  and  the  development  of  extensive  coal-bearing  formations. 
The  essential  features  are  base-leveling  of  the  higher  areas  with  a 
consequent  aggrading  and  leveling  up  of  the  lower  ones,  and  a  general 
slow  subsidence  of  the  areas  of  peat  deposition. 


THE  ORIGIN  OF  UNDERCLAYS  153 

The  Origin  of  Underclays 

Various  names  have  been  applied  to  the  clays  underlying  coal 
seams  such  as  the  "sole,"  "seatearth,"  and  "mur."  Some  seams 
have  no  distinct  underclay  and  some  even  lie  on  granite,  schist  or 
other  igneous  or  metamorphic  rocks.  Beneath  others  the  floor  of 
the  seam  is  conglomerate  or  coarse  sandstone,  and  limestone  under- 
lies a  few  beds.  In  many  seams  the  change  from  coal  to  barren  rock 
is  abrupt  while  in  others  there  is  carbonaceous  shale  or  black  slate 
lying  next  to  the  coal  indicating  a  gradual  transition  from  the  coal 
to  the  rocks  free  from  vegetal  matter.  The  shales,  being  less  porous, 
are  more  likely  to  have  partly  preserved  vegetation  in  them  than  the 
sandstones  are,  because  the  latter  permit  access  of  oxidizing  water 
which  decomposes  the  vegetal  matter  and  leaves  no  carbonaceous 
deposit.  The  change  thus  appears  more  abrupt  at  the  contact  with 
sandstone  than  it  really  was. 

Underclays  are  so  abundant  in  certain  coal  fields  that  some  early 
writers,  like  Logan,  regarded  them  as  a  universal  accompaniment  of 
coal  seams.  They  are  almost  everywhere  present  under  the  seams  of 
some  of  the  English  and  American  fields  of  Carboniferous  age  and 
they  have  been  regarded  by  some  writers  as  inseparably  connected 
genetically  with  the  seams.  Many  of  these  clays  are  fireclays  and 
they  are  of  great  economic  importance.  They  seldom  show  good 
stratification  which  may  be  at  least  partly  explained  by  their  plastic 
property,  permitting  them  to  be  squeezed  and  kneaded  under  pressure 
until  the  bedding  was  lost.  It  is  also  observed  that  a  layer  of  rock 
which  has  been  penetrated  by  innumerable  roots  usually  loses  its 
laminated  character. 

The  unstratified  character,  the  bleached  appearance,  and  the 
common  occurrence  of  Stigmaria,  or  roots  in  these  clays  has  led  many 
observers  to  regard  them  as  old  soils  on  which  the  vegetation  forming 
the  coal  seams  grew.  It  is  well  known  from  observation  that  the 
roots  of  plants  will  bleach  the  rocks  they  penetrate  and  these  under- 
clays  bear  a  certain  resemblance  to  the  muds  under  some  modern 
peat-bogs  and  swamps.  It  is  also  well  known,  however,  that  modern 
peat  does  not  grow  only  on  such  soils  but  it  may  be  found  on  sands, 
marls,  or  almost  any  kind  of  rock.  It  is  therefore  evident  that  under- 
clays  are  not  essential  to  the  growth  of  luxuriant  vegetation  and  the 
question  may  then  be  asked  whether  the  vegetation  is  essential  to 


154  THE  ORIGIN  OF   COAL 

the  development  of  the  underclays.  Some  writers  have  gone  so  far 
as  to  claim  that  where  coal  is  not  found  above  the  fireclay  it  has  been 
removed  by  erosion,  but  such  a  sweeping  statement  does  not  seem  to 
be  justified  because  fireclays  have  been  found  in  marine  deposits 
unassociated  with  coal  deposits  of  any  kind.  Most  of  those  clays 
are,  however,  stratified  and  laminated. 

If  the  drift  theory  were  to  be  accepted  for  the  accumulation  of  the 
vegetal  matter  these  clays  should  represent  a  deposit  of  the  finest 
and  most  completely  assorted  mineral  sediment  deposited  in  quiet 
water  just  before  the  lighter  vegetal  matter  settled  to  the  bottom. 
In  that  case,  however,  they  should  show  more  stratification  than 
they  do.  Arber1  suggests  that  they  are  marine  and  brackish  water 
oozes  deposited  in  estuaries  like  the  black  oozes  of  the  nipa  and  man- 
grove swamps  of  the  present  day.  If  this  be  so,  it  is  hard  to  under- 
stand why  they  are  found  only  in  their  present  position  with  reference 
to  the  coal.  If  coal  be  deposited  in  accordance  with  the  in  situ  theory 
then  these  clays  may  have  been  the  finer  material  which  filled  the 
basin  in  which  the  swamp  occurred  and  the  lack  of  stratification  re- 
sulted from  the  growth  of  the  plants  upon  it  and  later  movements  in 
a  semi-plastic  mass. 

There  is  one  other  possibility.  If  the  statement  of  Mietzsch  holds 
good  that  living  Lycopodiaceae  have  from  22  to  26  per  cent  of  clayey 
matter  in  their  ash  and  the  ancient  types  of  these  plants  had  a  similar 
proportion,  may  not  the  decay  of  vast  quantities  of  such  plants  on 
the  floor  of  a  swamp,  before  there  was  sufficient  water  over  the  vege- 
tal matter  to  prevent  decay,  have  produced  a  deposit  such  as  the 
underclay?  Some  efforts  have  been  made  to  compare  the  composi- 
tion of  the  ash  of  the  coal  with  that  of  the  fireclay  but  this  has  not 
proved  to  be  an  entirely  satisfactory  means  of  settling  the  question. 
The  clay  in  any  case  is  mineral  matter  and  there  is  always  more  or 
less  of  this  in  coal,  carried  in  by  wind  and  water  from  surrounding 
lands,  and  while  it  may  be  similar  to  that  in  the  plants  it  is  independ- 
ent of  the  composition  of  the  ash  of  the  wood.  It  is  probable  that 
some  clays  are  at  least  partly  chemical  sediments. 

There  is  much  need  of  further  information  regarding  these  inter- 
esting and  valuable  rocks.  It  seems  very  probable  that  the  clays 
were  deposited  as  part  of  a  normal  series  of  sediments  and  that 

1  Arber,  E.  A.  N.,  The  natural  history  of  coal,  p.  91,  1912. 


CLIMATIC   CONDITIONS  155 

the  growth  of  plants  helped  to  destroy  the  stratification  and  to 
extract  certain  of  the  soluble  salts;  but  the  plants  were  not  abso- 
lutely necessary  for  the  formation  of  the  clay  nor  was  that  kind  of 
clay  necessary  for  the  growth  of  the  vegetation  as  demonstrated  by 
modern  swamps  and  peat-bogs. 

Climatic  Conditions 

Concerning  the  climate  of  the  coal-forming  periods  there  is  some 
difference  of  opinion  among  paleobotanists.  They  are  our  chief 
judges  in  this  discussion  because  we  are  dependent  mainly  upon  the 
plants  of  those  periods  for  indications  of  climatic  conditions.  There 
is  one  feature,  however,  concerning  which  there  is  unanimity  among 
all  the  best  authorities,  and  that  is  that  the  climate  was  uniform  over 
great  areas  of  the  earth's  surface.  This  is  demonstrated  by  the 
fact  that  the  same  genera  and  some  of  the  same  species  of  plants  of 
Carboniferous  age  are  found  distributed  over  both  hemispheres  from 
the  tropical  to  the  polar  regions.  A  similar  condition  prevailed  again 
in  Jurassic  and  Cretaceous  times.  As  to  the  cause  of  this  uniformity 
little  is  definitely  known.  It  has  been  suggested  by  some  geologists 
and  botanists  that  this  condition  was  due  to  a  greater  amount  of 
carbon  dioxide  in  the  air  than  there  is  in  normal  times  and  Cham- 
berlin1  has  described  in  detail  how  its  presence  might  be  brought 
about.  Other  factors  which  might  aid  in  producing  this  uniform 
condition  are  the  relation  between  sun  and  earth  in  position  and  dis- 
tance and  changes  in  the  distribution  of  land  masses  in  the  sea,  per- 
mitting warm  ocean  currents  to  reach  the  polar  regions  and  melt 
the  ice. 

There  is  also  little  doubt  concerning  the  humidity  of  the  atmosphere 
during  the  coal- forming  periods.  This  is  necessary  for  the  growth 
of  such  enormous  quantities  of  plants  in  order  that  they  may  give 
rise  to  coal.  Humidity  and  uniformity  in  climate  are  rather  closely 
related.  Further,  if  we  accept  the  in  situ  theory  for  the  origin  of 
coal,  sufficient  water  to  cover  the  fallen  vegetation  is  essential  for 
its  preservation  and  the  warmer  the  climate  the  more  the  water  re- 
quired. 

As  to  whether  the  climate  in  the  Carboniferous  and  other  great 
periods  of  peat  formation  was  hot  is  a  debated  question  among  paleo- 

1  Chamberlin  and  Salisbury.     Geology,  Vol.  Ill,  p.  432,  1906. 


156  THE   ORIGIN  OF  COAL 

botanists.  Arber1  claims  that  there  is  nothing  in  the  Carboniferous 
flora  so  far  as  known  to  prove  that  it  was  tropical  in  character,  as 
luxuriant  forests  may  be  found  today  in  temperate  regions  and  the 
large  cells  of  the  plants  do  not  necessarily  indicate  tropical  conditions. 
White2  believes  that  the  climate  was  humid,  uniform  and  mild,  being 
generally  either  tropical  or  sub-tropical.  Some  evidences  of  these 
conditions  are  the  similarity  in  character  between  many  of  the  plants 
now  found  in  tropical  swamps  and  those  found  in  coal  formations. 
The  absence  of  growth  rings  in  the  trees  indicates  uniformity  in  seasons 
and  the  wide  distribution  of  almost  identical  floras  indicates  uniform- 
ity in  climate  over  wide  areas  of  the  globe.  The  large  leaves  and 
fronds,  and  the  large  cells  with  thin  walls  indicate  rapid  growth.  The 
stomata  are  protected  in  grooves  on  the  under  sides  of  leaves  of  many 
plants  and  subaerial  roots  are  found  on  many  species.  The  seeds 
show  provision  for  flotation  and  delayed  fertilization.  The  presence 
of  tree  ferns,  palms,  and  cinnamon  trees  in  the  Tertiary  coal  deposits 
suggests  tropical,  or  at  least  sub-tropical  conditions. 

There  is  one  rather  peculiar  association  of  plants  known  as  the 
Gangamopteris,  or  Glossopteris  flora,  which  in  Permian  time  spread 
widely  over  the  Southern  Hemisphere.  It  is  different  from  the 
other  coal-formation  floras  because  of  its  close  association  with  glacia- 
tion.  It  is  found  in  Australia,  India,  South  Africa,  South  America, 
and  to  some  extent  in  Russia,  where  Glossopteris  and  Gangamop- 
teris are  abundant  in  the  vicinity  of  Moscow. 

In  Australia  the  Permo-Carboniferous,  or  possibly  more  strictly, 
the  Permian  system,  forms  a  very  thick  group  of  rocks  containing 
extensive  coal  seams,  which  are  of  fresh- water  origin  and  which  in 
most  cases  show  evidences  of  autochthonous  origin  by  the  presence  of 
roots  in  the  underlying  clays.  This  group  also  contains  thick  beds 
of  tillite  showing  that  glacial  conditions  were  prevalent  at  that  time 
and  that  there  were  at  least  two  great  interglacial  periods.  A  con- 
densed description  of  these  rocks  taken  from  David's  work  is  as 
follows:3 

1  Arber,  E.  A.  N.,  The  natural  history  of  coal,  Cambridge  University  Press,  p.  70, 1912. 

2  White,  David,  The  origin  of  coal,  U.  S.  Bur.  of  Mines,  Bull.  38,  p.  68,  1913. 

3  David,  T.  W.  E.,  British  Ass.  Adv.  Sci.  Handbook  for  Australia,  p.  257,  1914.     See 
also  Siissmilch,  C.  A.    An  introduction  to  the  Geology  of  New  South  Wales,  p.  93,  Sydney, 
1914. 


TRANSFORMATION  OF  VEGETAL  MATTER  INTO   COAL          157 

Thickness 
Ft. 

1.  Acid  granites  of  New  England 

2.  Upper  or  Newcastle  coal  measures;  with  35  to  40  feet  of  workable 

coal.  Glossopteris  predominates  over  Gangamopteris.    Dadoxy- 

lon  abundant 1500 

3.  Dempsey  Series;  Barren  fresh- water  shale 2200 

4.  Middle  coal  measures;  with  20  feet  of  workable  coal 500-1800 

5.  Upper  Marine  Series;  with  marine  fossils  and  glacial  erratics ...  6400 

6.  Lower  or  Greta  coal  measures;  with  about  20  feet  of  workable  coal. 

Gangamopteris  predominates  over  Glossopteris 100-300 

7.  Lower  Marine  Series;    with  marine  fossils.     Basalts  and  tuffs. 

Glacial  beds  300  feet  thick  at  base 4800 

At  Bacchus  Marsh,  Victoria,  there  are  four  beds  of  tillite  in  a  for- 
mation 2000  feet  thick.  These  glacial  beds  have  been  correlated  with 
the  Dwyka  conglomerates  of  South  Africa.  In  one  place  Ganga- 
mopteris occurs  with  a  local  coal  seam  in  the  upper  part  of  the  Lower 
Marine  series,  in  fresh-water  deposits. 

So  far  as  known  the  Glossopteris  flora  does  not  occur  in  the  typically 
Carboniferous  strata  which  reach  20,000  feet  in  thickness  in  Australia, 
nor  is  Lepidodendron  found  in  the  Permo-Carboniferous  although 
prevalent  in  the  Carboniferous  and  upper  Devonian.  No  doubt  the 
great  change  in  climate  was  too  severe  a  test  for  Lepidodendron  and 
related  plants  and  they  disappeared  during  the  glacial  conditions. 

Although  there  were  two  glacial  periods  associated  with  the  coal 
seams  of  the  Permian,  there  is  no  evidence  that  there  was  a  sudden 
change  in  climate  and  that  the  Glossopteris  and  Gangamopteris 
flora  lived  under  frigid  conditions.  These  glacial  epochs  were  separ- 
ated by  long  periods  of  time  and  when  it  is  considered  that  during 
the  apparently  much  shorter  interglacial  periods  of  the  Pleistocene 
in  America  such  trees  as  the  pawpaw  (Asiminia  triloba)  and  the  osage 
orange  (Madura  arantiaca),  now  found  only  considerably  farther 
south,  grew  at  Toronto,  Canada,1  it  seems  probable  that  Australia 
may  still  have  had  a  reasonably  mild  climate  during  the  formation 
of  the  important  coal  seams  of  Permian  age. 

The  Transformation  of  Vegetal  Matter  into  Coal 

It  is  generally  recognized  that  when  vegetation  changes  to  coal  it 
passes  through  two  stages,  the  first  being  known  as  the  biochemical 
and  the  second  as  the  dynamochemical  stage.  As  these  terms  indicate, 

1  Coleman,  A.  P.,  Interglacial  fossils  from  the  Don  Valley,  Toronto.  Amer.  Geol. 
Vol.  XII,  p.  86,  1894. 


158 


THE  ORIGIN  OF  COAL 


the  first  process  is  due  chiefly  to  the  action  of  bacteria  and  other  low 
forms  of  life  and  the  second  to  geological  forces  capable  of  produc- 
ing chemical  and  physical  changes  in  the  vegetal  matter. 

The  biochemical  process,  or  the  first  stage  in  coal  formation.  — 
When  plants  in  a  bog  or  swamp  cease  to  grow,  and  fall,  they  are 
subject  to  attacks  from  bacteria  and  other  low  organisms.     The 
most  extensive  investigations  on  this  subject  have  been  carried  on 
by  Renault,1  the  French  scientist,  who  spent  most  of  his  later  years 


I  J 

FIG.  31.  —  Bacteria  in  the  cuticle  of  bothrodendron  from  the  "paper  coal"  (x  800)  (a) 
Bacillus  exiguees  (b)  Isolated  micrococcus  (c)  Micrococcus  in  process  of  division  (d)  Micro- 
coccus  in  colonies  (e)  Spores  of  bacilli.  (After  Renault.) 

in  studying  and  identifying  new  species  of  bacteria  in  the  coals.  It 
is  unfortunate  that  when  Renault  did  such  excellent  work  on  this 
subject  he  should  have  permitted  himself  to  go  to  extremes  in  his 
ideas  of  the  prevalence  and  importance  of  these  fossil  organisms  in 
the  coal.  Having  had  the  privilege  of  examining  his  original  slides 
the  writer  is  convinced  that  many  objects  taken  for  bacteria  were 
specks  of  mineral  matter  and  in  some  cases,  at  least,  crystallized  or- 
ganic matter.  Similar  conclusions  have  been  reached  by  others 
who  have  investigated  this  subject.  Renault  has  shown,  however, 

1  Renault,  B.,  Loc.  cit.  Also  du  role  de  quelques  bacteriace'es  fossiles  au  point  de 
vue  geologique.  Congres  Geologique  International,  pp.  646-663,  1900. 


THE   BIOCHEMICAL  PROCESS 


159 


that  a  great  many  bacteria  have  been  sufficiently  well  preserved  to  be 
recognized  and  to  show  that  they  undoubtedly  did  a  great  deal  to 
macerate  the  vegetal  matter  (Figs.  31  and  32).  There  have  been 
recognized  representatives  of  the  living  forms  such  as  Micrococcus 
and  Streptococcus  in  ad-  r  miTTim 

dition  to  many  others. 
These  forms  were  most 
active  in  the  upper 
layers  of  the  peat  be- 
cause the  lower  portions 
of  the  bog  were  so 
charged  with  organic 
solutions  of  ulmic,  crenic 
and  other  acids  resulting 
from  chemical  action 
that  the  bacteria  could 
scarcely  exist.  Although 
no  quantitative  study 
has  been  made  of  this 
subject  it  is  believed 
that  their  action  extends 
to  comparatively  shallow 
depths. 

In    addition    to    the 
bacteria  there  are  many 


) 


FIG.  32.  —  Chains  of  bacilli  in  coal  of  arthropitus 
(x  1200)  (a)  Chainlet  of  bacilli  mostly  diplospores 
(b)  Group  of  arthrospores  (c)  Chain  beginning  to 
ramify.  (After  Renault.) 


larger  plants,  especially 
the  fungi,  which  help  to 
produce  chemical 
changes  and  aid  in  the 
maceration  of  the  plant  debris.  Among  these,  mushrooms  and  related 
plants  probably  play  an  important  role.  The  action  in  all  cases 
seems  to  result  in  a  change  from  the  production  of  oxygenated  hy- 
drocarbon compounds  of  the  living  plant  to  a  breaking  up  of  these 
into  such  simple  compounds  as  the  oxides  of  carbon.  When  the 
latter  compounds  are  formed  the  hydrogen  must  then  be  free  to  form 
simple  compounds  with  carbon  and  with  oxygen  such  as  methane,  and 
water. 
In  addition  to  the  bacterial  action  being  halted  by  acid  compounds 


160  THE  ORIGIN  OF  COAL 

resulting  from  their  own  action,  it  may  be  stopped  by  burial  of  the 
peat  under  layers  of  sediment  or  by  mineral  matter,  deposited  from 
solution,  surrounding  the  plant  debris.  The  latter  action  is  well 
illustrated  by  the  concretions  commonly  called  "coal  balls"  found 
in  many  seams,  or  in  the  rocks  overlying  them.  These  bodies  fre- 
quently contain  perfectly  preserved  plant  remains  showing  that  the 
mineral  matter  must  have  sealed  them  up  almost  immediately  after 
they  fell. 

The  second  stage  in  codification:  It  seems  to  be  generally  admitted 
that  biochemical  processes  are  responsible  for  the  early  stages  in  the 
alteration  of  the  plant  debris  as  it  changes  to  coal  of  any  kind  or  even 
to  old  compact  peat.  There  is  a  much  greater  divergence  of  opinion, 
however,  regarding  the  processes  which  continue  the  alteration  until 
different  varieties  of  coal  result.  Since  the  greater  number  of  ob- 
servers consider  that  the  second  stage  is  produced  almost  entirely 
by  dynamochemical  action  this  stage  in  the  process  is  very  frequently 
discussed  as  if  the  dynamochemical  were  the  only  factor  to  be  taken 
into  consideration,  but  several  other  hypotheses  have  been  advanced 
in  opposition  to  the  dynamochemical  theory. 

The  various  suggestions  to  account  for  the  development  of  different 
varieties  of  coal  from  vegetal  matter  may  be  summed  up  as  follows: 
(i)  Differences  in  kinds  of  vegetation  and  differences  in  climates  in 
different  regions.  (2)  The  length  of  time  during  which  the  vegetation 
has  been  exposed  before  burial  by  sediments.  (3)  Length  of  time; 
since  burial  of  the  vegetation.  (4)  The  depth  of  burial  of  the  vege- 
tation. (5)  Action  of  heat  from  compression  or  from  intrusions  of 
igneous  rocks.  (6)  Possibility  of  escape  of  volatile  constituents  after 
burial  beneath  sediments  because  of  fractures  or  pores  in  the  over- 
lying rocks,  and  jointage  in  the  coal  seams.  (7)  The  pressure  re- 
sulting from  compression  of  the  seam  during  dynamic  changes  in  the 
enclosing  rocks. 

1.  Different  kinds  of  vegetation  and  different  climates.  —  An 
examination  of  the  different  varieties  of  coal,  omitting  special  types 
like  cannel,  will  show  that  they  differ  very  little  in  their  physical 
composition.  They  all,  whether  lignite  or  anthracite,  contain  light 
and  dark  bands,  fragments  of  resin,  spores,  fragments  of  bark  and 
other  plant  debris.  This  seems  to  indicate  that  they  may  have  been 
derived  from  the  same  type  of  vegetation.  Anthracite  has  not  been 


DIFFERENT  KINDS  OF  VEGETATION  AND   CLIMATES 


161 


shown  to  contain  a  greater  proportion  of  spores,  resin  or  other  portions 
of  the  plant  than  bituminous  coal.  It  is  well  demonstrated  that  in 
an  anthracite  region  a  seam  will  be  anthracite  throughout  and  not 
in  patches  only  like  the  cannel  in  bituminous  coal  seams.  The  fol- 
lowing analyses  will  show  that  various  types  of  trees  are  so  nearly 
alike  in  chemical  composition  that  it  would  be  impossible  to  put 
them  through  the  same  geological  processes  and  expect  to  get  different 
kinds  of  coal  from  them. 


Wood 

Ash 

C 

H 

N 

Calorific 
power 

Oak                         

0.37 

50.16 

6.03 

4,620 

Ash                        

0.57 

4Q.i8 

6.27 

4,711 

Hornbeam         

o.  50 

48.99 

6.  20 

4,728 

Beech         

0.57 

4Q.o6 

6.  ii 

0.09 

4,770 

Birch          

0.29 

48.88 

6.06 

O.IO 

4,771 

Fir           

0.28 

50.36 

5-29 

0.05 

5,035 

Pine        

0.37 

50.31 

6.20 

0.04 

5,085 

Cellulose                                   

44-4 

6.2 

•*'     o 

4,140 

Table  by  Gottlieb. 
&Co. 


From  Cellulose,  by  Cross  and  Be  van.     Longmans,  Green 


Plant 

C 

H 

0 

N 

Ash 

i.  Lycopodium  dendroideum  
3.  Lycopodium  complanatum  .  .  .  . 
5    Equisetum  hyemale  

47.11 
45-78 

41    Q4 

6-39 
6.25 
5-8q 

41.85 
40.66 
•?Q  .23 

.40 

.84 

.  12 

3-25 
5-47 
II  .82 

7.  Asidium  marginale  

44  77 

c   no 

41  .97 

.08 

c.iq 

9.  Cyathea  camculata  

4?  .  ?o 

6.  II 

30.82 

.  12 

7.56 

n.  Cyathea  caniculata  

48.72 

4.89 

38.48 

.42 

6.4Q 

Analyses  by  G.  W.  Hawes.1  Nos.  1,3,5  and  7  are  average  samples  of  the  part 
of  the  plant  above  ground,  including  spores.  Nos.  9  and  n  are  tree  ferns  from 
Tahiti.  No.  9  is  an  analysis  of  a  section  of  the  stem  and  No.  n  of  the  cortical 
part. 

Analyses  of  coal  derived  from  different  genera  of  Carboniferous 
trees  were  made  by  Carnot  and  it  can  be  seen  that  the  differences  in 
composition  in  coal  from  Lepidodendron,  Cordaites  or  Ptychopteris 
are  negligible,  the  maximum  difference  in  carbon  being  only  2.66 
per  cent  and  in  hydrogen  0.03  per  cent. 

The  plant  fossils  were  identified  by  Renault  and  carefully  selected 

1  Hawes,  G.  W.,  On  the  chemical  composition  of  the  wood  of  acrogens.  Amer.  Jour. 
Sci.  (3rd  Series)  Vol.  7,  p.  585,  1874. 


162  THE  ORIGIN  OF  COAL 

to  obtain  any  differences  in  the  coal  which  might  be  due  to  differences 
in  the  original  vegetation. 

It  can  be  concluded  that  different  types  of  plants  cannot  produce 
any  material  difference  in  the  nature  of  the  coal  formed  and  that  they 
have  no  particular  bearing  on  the  origin  of  anthracite.  It  is  recog- 
nized, however,  that  different  portions  of  the  plant  such  as  spores 
or  resin,  the  latter  of  which  may  contain  over  80  per  cent  of  carbon, 
may  form  different  types  of  coal  if  separated  from  the  other  plant 
debris  and  segregated  in  sufficiently  large  masses.  There  is,  how- 
ever, no  evidence  whatever  that  such  has  been  the  case  in  the  for- 
mation of  anthracite. 

As  for  differences  in  climate  producing  any  marked  variation  in 
the  coal  of  different  regions,  there  is  no  ground  for  accepting  such  a 
theory  as  all  vegetation  must  be  covered  with  water  to  preserve  it. 
There  is  no  great  difference  in  the  peat  formed  from  trees  in  the 
tropical  and  temperate  zones. 

2.  Exposure  before  burial.  —  It  is  a  recognized  fact  that  if  wood  be 
exposed  to  the  air  certain  portions  will  decompose  before  other  por- 
tions and  there  will  be  a  relative  increase  in  carbon  and  a  decrease  in 
hydrogen  and  oxygen.  The  wood  usually  decomposes  first  and  leaves 
the  more  resistant  bark  and  related  tissues.  To  illustrate  the  change 
which  occurs,  the  following  analyses  are  quoted  from  Fayol's  work.1 

Carbon  in  bark  of  oak,  29.65  per  cent;  in  sound  wood  21.95  to  22.82 
per  cent;  in  the  same  tree,  slightly  decomposed,  24.75;  more  decom- 
posed, 27.60;  and  rotten,  31.00  per  cent.  Analyses  by  Pollard  of 
dark  and  bright  coal  from  a  seam  in  Wales  show  carbon  in  bright 
band  63.96,  and  in  dull  powder  77.17  per  cent,  and  since  the  dull 
layers  of  mineral  charcoal  are  generally  thought  to  have  originated 
through  extensive  rotting  of  the  vegetation  before  burial  these  figures 
show  that  there  undoubtedly  may  be  considerable  difference  produced 
in  the  composition  of  the  resulting  material  by  more  prolonged  ex- 
posure before  burial.  When  one  attempts  to  employ  this  as  a  means 
of  explaining  the  origin  of  the  great  deposits  of  anthracite  it  is  useless, 
however,  because  these  dull  layers  are  present  in  bituminous  coal  also, 
and  they  are  distributed  throughout  the  anthracite  seams  in  such  a 
way  as  to  indicate  that  they  have  no  bearing  on  the  anthracitic  char- 
acter of  the  seam  taken  as  a  whole. 

1  Fayol,  H.  Loc.  cit,  p.  171. 


LENGTH  OF   TIME  SINCE   BURIAL  163 

It  has  been  suggested  that  the  anthracite  field  of  Pennsylvania 
owes  its  origin  to  longer  exposure  of  vegetation  laid  down  in  the  east- 
ern part  of  the  state  than  that  deposited  in  the  west  because  of  a 
gradual  migration  westward  of  the  coastal  plain  on  which  the  plants 
grew.  This  assumption  scarcely  seems  justified  because  it  is  probable 
that  the  swamp  or  swamps  which  gave  rise  to  the  Pennsylvanian  coal 
deposits  were  spread  pretty  uniformly  over  the  anthracite  and  bitumi- 
nous areas  at  the  same  time.  Further,  the  anthracite  region  being 
closer  to  Appalachia,  the  main  source  of  supply  for  clastic  sediments, 
it  is  probable  that  the  vegetation  was  buried  early  in  the  history  of 
these  deposits  In  their  studies  of  the  South  Wales  anthracite  de- 
posits Strahan  and  Pollard  state  that  no  definite  relation  exists  be- 
tween the  position  of  the  anthracitized  beds  and  the  old  shore- 
line. 

3.  Length  of  time  since  burial.  —  A  general  impression  exists  among 
many  people  interested  in  coal  that  the  ag£  of  the  coal  has  an  impor- 
tant bearing  on  its  quality.  To  a  certain  degree  this  assumption  is 
correct,  because,  other  things  being  equal,  the  older  coals  will  be 
higher  in  the  peat-to-anthracite  scale  than  the  younger  ones,  not 
simply  because  the  vegetation  was  formed  in  any  particular  geologic 
period,  but  because  the  metamorphosing  processes  have  had  longer 
to  work  and  the  older  rocks  have  as  a  rule  been  more  deeply  buried 
and  subjected  to  greater  pressures  than  the  younger  rocks.  There 
are  many  examples  on  record  where  seams  of  Carboniferous  age  are 
still  in  the  form  of  brown  coal  or  lignite.  Such  a  case  is  found  in 
Western  Australia  where  a  small  area  of  Permo- Carboniferous  meas- 
ures was  faulted  up  and  preserved  from  intense  pressure.  The  coal 
is  still  brown  coal,  although  practically  all  other  Penno-Carbonifer- 
ous  coal  in  Australia  is  bituminous  or  anthracite  In  Russia  brown 
coal  occurs  in  the  Mississippian,  or  Lower  Carboniferous,  while  in  the 
western  states  and  Canada  and  in  many  other  countries  the  Cretaceous 
and  Tertiary  coals,  which  are  more  typically  lignite,  have  been  altered 
to  high-grade  bituminous  coal  or  even  anthracite  in  local  areas. 

In  connection  with  this  discussion  on  the  length  of  time  since 
burial  of  the  vegetal  matter,  the  question  of  the  length  of  time  a  bed 
of  vegetation  must  be  buried  before  it  is  changed  to  coal  may  be  con- 
sidered. We  have  very  little  definite  information  on  this  subject 
but  there  is  a  clue  in  the  occurrence  of  coal  pebbles  in  the  rocks  asso- 


164  THE  ORIGIN  OF   COAL 

dated  with  coal  beds.  Renault  and  Fayol1  have  discussed  the  coal 
grains  and  pebbles  in  the  Coal  Measures  in  the  Commentry  basin  in 
France.  That  these  are  water-borne  fragments  of  coal  and  not  frag- 
ments of  wood  buried  in  the  sandstones  and  conglomerates  and  later 
transformed  into  coal  is  indicated  by  the  fact  that  they  have  not 
shrunk  nor  have  they  been  deformed  in  shape  as  they  would  have 
been  had  they  consisted  of  wood  and  been  turned  into  coal  after  their 
burial.  They  must  represent  fragments  of  a  deposit  lower  in  the 
Carboniferous  which  had  already  changed  to  coal  and  been  broken  up 
by  erosion. 

In  England  there  are  also  pebbles  of  coal  high  up  in  the  Coal  Meas- 
ures which  Strahan  considers  as  distinct  fragments  of  coal  derived 
from  an  eroded  coal  seam  lying  a  few  feet  below  the  Pennant  grit 
which  carries  the  pebbles.  There  is  no  older  coal  formation  in  the 
region  which  could  urnish  these  pebbles.  These  examples  indicate 
that  coal  must  form  quite, rapidly  from  the  vegetation. 

As  modern  examples  of  wood  changing  to  coal  in  very  short 
spaces  of  time,  a  case  occurring  in  the  vicinity  of  Scranton,  Penn- 
sylvania, is  cited  by  Moffat.2 

A  mine  prop  left  standing  and  surrounded  by  mine  refuse  was  sub- 
jected for  about  30  years  to  high  pressure  from  the  roof  and  to  high 
temperature  from  a  mine  fire,  although  the  fire  did  not  actually  reach 
the  prop.  Different  parts  of  the  prop  suffered  varying  degrees  of 
alteration  The  lower  portion  was  well  preserved  wood;  about  half- 
way up  it  was  a  little  charred  externally  and  above  this  it  was  turned 
into  friable,  soft  charcoal.  The  upper  part  and  especially  the  cap 
wedge,  which  had  suffered  from  great  compression  and  had  been 
crushed  down,  was  greatly  altered  and  had  a  conchoidal  fracture  like 
anthracite  coal,  a  jet  black  color,  a  bright  glossy  luster,  and  a  specific 
gravity  of  1.38.  It  burned  with  a  feeble  flame.  Analyses  showed 
that  it  contained:  Moisture  at  100°,  5.65;  Volatile  Matter,  43.05; 
Fixed  Carbon,  51.00;  and  Ash,  0.30  per  cent.  It  would  appear  that 
although  heat  aided  this  change  the  pressure  was  necessary  to  produce 
the  coaly  character,  as  distinguished  from  charcoal.  The  wood  in 
this  prop  and  wedge  retained  its  structure  very  well. 

1  Op.  cit. 

2  Moffat,  E.  S.,  Note  on  the  formation  of  coal  from  mine  timber,  Trans.  Amer.  Inst. 
Min.  Eng.,  Vol.  15,  p.  819,  1886. 


ii 


§2 


1 1 

^  I 


.«  .9 


.s 


1 66  THE  ORIGIN  OF  COAL 

Daubree1  and  Fremy  have  produced  materials  resembling  coal 
from  various  woody  constituents  at  temperatures  from  200°  to  300°  C. 
It  was  found  that  woody  fibers,  as  vasculose  and  cellulose,  became 
black  and  brittle  but  retained  their  organization  and  did  not  fuse; 
while  such  substances  as  starch,  sugar,  gums,  and  chlorophyll  became, 
when  subjected  to  heat  and  pressure,  black,  brilliant,  and  insoluble 
like  coal.  The  latter  substances  will  also  leave  a  coke.  This  may 
account  for  some  of  the  differences  between  lignite  and  black  lignite, 
or  subbituminous  coal,  the  one  originally  having  more  woody  material 
than  the  other. 

From  all  available  evidence  it  would  appear  that  coal  may  form  in 
a  very  short  time,  geologically  speaking,  if  conditions  be  favorable. 
The  chief  factors  producing  the  change  are  heat  and  pressure. 

4.  Depth  of  burial.  —  The  depth  of  burial  is  so  closely  related  to 
the  compression  resulting  from  crustal  movements  that  these  two 
factors  may  be  considered  together.  It  should  be  pointed  out,  how- 
ever, that  there  are  few,  if  any,  cases  where  it  can  be  shown  that  the 
depth  of  burial  alone  was  sufficient  to  produce  anthracite,  although 
it  is  such  a  generally  recognized  principle  that  the  fixed  carbon  in- 
creases and  the  volatile  matter  decreases  with  depth  in  a  series  of  seams 
that  this  principle  is  commonly  known  as  the  Law  of  Hill,  after  the 
man  who  expounded  it.  It  has  been  stated  by  some  writers  that 
there  is  a  definite  relation  between  the  depth  of  the  seams  and  the 
anthracitization  of  the  coal  in  the  basin  of  Commentry  in  France, 
but  this  statement  will  not  hold  in  all  cases.  Strahan2  has  pointed 
out  that  in  the  South  Wales  field  the  cover  of  not  only  the  Palaeozoic 
rocks  but  also  of  the  later  rocks  over  the  bituminous  field  is  much 
thicker  than  that  over  the  anthracite  field.  He  states  further,  how- 
ever, that  in  general  the  conclusion  of  De  la  Becke  and  Joseph  that 
the  lower  seams  in  the  anthracite  field  were  more  anthracitic  than  the 
upper  was  correct  but  this  will  not  hold  for  all  seams  throughout  the 
field.  The  chart  of  iso-anthracitic  lines  (Figs.  33  and  34)  brings  out 
clearly  the  relation  between  the  various  seams  in  this  field.  White3 

1  Daubree,  fitudes  et  experiences  synthetiques  sur  le  metamorphisme  et  sur  le  for- 
mation des  roches  crystallines,  p.  72,  1860. 

2  Strahan,  A.,  and  Pollard,  W.,  The  coals  of  South  Wales,  with  special  reference  to 
the  origin  and  distribution  of  anthracite.     Memoirs  Geol.  Survey,  England  and  Wales, 
2nd  Ed.,  pp.  73  and  74,  1915. 

»  White,  D.,  Op.  cit.,  p.  126. 


DEPTH  OF   BURIAL 


167 


has  pointed  out  that  of  20  cases  where  two  or  more  of  these  seams  were 
vertically  100  feet  or  more  apart  the  analyses  show  only  one  case 
where  there  was  a  downward  increase  of  volatile  matter.  Two  cases 
show  no  difference  and  the  others  show  an  average  loss  per  100  feet 
of  descent  of  0.6  per  cent  volatile  matter.  In  American  seams,  out  of 
thirty-four  cases  twenty-nine  show  an  average  decrease  of  0.38  per 
cent  volatile  matter  per  100  feet  descent.  Quoting  from  Van  der 
Gracht,  White  states  that  at  Helenaveen  the  decrease  in  the  gas  coal 
is  about  0.53  per  cent;  at  Helden  in  the  coking  coal  about  0.8  per 
cent;  at  Baarlo  about  0.62  per  cent;  and  in  Westphalia,  0.51  per 


FIG.  34.  —  Relation  between  depth  and  the  carbon-hydrogen  ratios  in  three  seams 
in  the  South  Wales  coal  field.     (After  Strahan  and  Pollard.) 

cent  for  gas  coal  and  0.71  per  cent  for  coking  coal  per  100  feet.  In 
Pennsylvania  the  depth  of  the  anthracite  seams  cannot  be  taken  as 
a  criterion  for  the  alteration  which  the  coal  has  undergone  but  in 
some  of  the  semianthracite  areas  of  China  there  seems  to  be  a  more 
marked  connection  between  the  depth  at  which  the  seams  lie  and  the 
degree  of  anthracitization  There  must,  however,  also  be  taken  into 
consideration  the  factor  of  thrust,  a  subject  which  will  be  discussed 
later. 


1 68  THE  ORIGIN  OF   COAL 

5.  Effects  of  heat.  —  That  heat  from  igneous  rocks  aided  by  the  pres- 
sure which  must  be  an  accompaniment  of  intrusions  can  produce  an- 
thracite from  bituminous  coal  has  been  proven  beyond  a  doubt.  In 
Colorado,  Alaska,  New  Mexico,  and  in  numerous  countries,  natural 
coke,  anthracite,  and  other  types  of  coal  have  been  produced  from 
bituminous  coal  by  igneous  rocks.  The  effects  of  igneous  intrusions 
are,  however,  quite  local  and  they  have  not  been  responsible  for  the 
anthracite  in  the  great  fields  of  South  Wales  and  Pennsylvania.  In 
the  Cerrillos  Coal  Field  of  New  Mexico,  considerable  anthracite, 
mostly  of  secondary  grade,  has  been  produced  as  a  result  of  the  in- 
trusion of  a  great  sill  about  400  feet  thick  along  the  surface  of  a  coal 
seam,  but  the  effects  extend  only  a  comparatively  short  distance  from 
the  sill.  As  a  rule  there  is  some  relation  between  the  width  of  a  dike 
or  thickness  of  a  sill  and  the  width  of  the  zone  of  coal  affected,  but 
this  varies  greatly.  Usually  the  coal  is  not  affected  much  beyond 
the  width  of  the  dike.  It  should  be  remembered  in  this  connection 
that  an  igneous  rock  intruding  coal  will  affect  it  much  as  it  does  other 
rocks  which  it  intrudes.  In  some  cases  a  dike  or  sill  will  scarcely 
metamorphose  the  adjacent  rocks  due  to  the  fact  it  was  almost  cooled 
when  it  reached  them  or  it  may  have  had  little  hot  gas  or  water  to 
give  off  to  attack  the  adjacent  rocks.  Some  intruding  rocks  were 
hot  and,  carrying  much  hot  gas  and  water,  were  capable  of  profoundly 
altering  the  surrounding  rocks.  As  a  rule  acid  rocks,  such  as  granites 
and  rhyolites,  are  capable  of  existing  in  the  liquid  condition  at  lower 
temperatures  than  the  basic  rocks  like  gabbros  and  basalts  or  traps, 
but  they  usually  carry  more  liquids  and  gases  and  are,  therefore, 
capable  of  producing  more  metamorphism  at  the  temperature  of 
intrusion  than  are  rocks  without  these  agents. 

In  1869  Bevan1  attempted  to  explain  the  origin  of  the  South  Wales 
anthracite  as  due  to  trap  rocks  but  it  has  been  shown  that  these 
igneous  rocks  were  earlier  than  the  coal  seams.  The  formation  of 
Pennsylvania  anthracite  has  also  been  assigned  to  the  heat  of  igneous 
intrusions  but  there  are  no  intrusions  worth  mentioning  in  this  coal 
field  and  those  intrusions  which  do  occur  are  Triassic  in  age  and  much 
later  than  the  coal.  Intrusions  of  the  same  age  and  character  occur 
also  in  the  bituminous  field  of  Pennsylvania  without  appreciably 
affecting  the  bituminous  character  of  the  coal.  It  must  be  admitted 
1  Bevan,  J.  P.,  The  geologist,  Vol.  II,  p.  75,  1869. 


ESCAPE  OF  VOLATILE   CONSTITUENTS  169 

that  the  influence  of  igneous  rocks  is  very  limited  although  neverthe- 
less real. 

6.  Escape  of  volatile  constituents  through  fractures  and  pores.  — 
In  order  to  explain  the  lack  of  anthracitization  of  coal  in  areas  of 
intense  folding  and  even  where  the  temperature  has  been  rather  high, 
Campbell1  has  suggested  that  fractures  such  as  joints  or  cleavage 
in  the  coal  and  adjacent  rocks  have  been  responsible  for  this  process. 
He  assumed  that  the  transformation  of  one  type  of  coal  to  another, 
higher  in  fixed  carbon,  was  primarily  due  to  heat  although  not  neces- 
sarily to  a  high  temperature  and  that  time  was  a  very  important 
factor  in  connection  with  the  results  derived  from  heating.  Pressure 
may  be  important  in  producing  heat  by  compression  and  in  aiding 
the  driving  off  of  the  volatile  constituents  but  unless  there  be  a  means 
of  escape  for  these  there  cannot  be  much  change  in  the  coal  either 
from  compression  or  heating.  The  process  may  operate  if  the  en- 
closing rocks  be  porous,  and  overlying  coarse  sandstones  would  be 
much  more  favorable  than  shales  for  the  escape  of  volatile  constituents. 
In  support  of  this  principle  he  cites  the  graphitic  coal  of  Rhode  Island 
as  an  example  of  coal  carried  to  the  extreme  condition  of  carbon- 
ization because  of  extensive  fracturing  permitting  escape  of  volatile 
constituents.  The  anthracite  of  Pennsylvania  is  more  fractured  than 
the  bituminous  coal,  and  the  lignites  of  North  Dakota  and  Texas  are 
overlain  by  impervious  clays.  This  hypothesis  is  said  to  apply 
equally  well  to  all  the  coal  fields  studied  in  the  United  States. 

Since  there  is  no  doubt  that  the  coal  changes  to  a  higher  carbon 
type  by  loss  of  gases  Campbell's  principle  is  perfectly  logical  but 
there  are  some  limitations  which  should  be  kept  in  mind,  and  this 
may  explain  why  some  highly  fractured  coal  has  not  been  altered  to 
a  high  carbon  type.  The  extensive  fracturing  of  a  rock  is  evidence  of 
yielding  to  stress,  and  the  pressure  which  would  have  been  exerted  on 
the  coal,  if  the  rock  had  not  been  broken,  is  relieved  by  fracturing, 
with  the  result  that  both  heat  and  pressure  are  lost.  There  is  ap- 
parently a  proper  balance  between  the  length  of  time  the  coal  suffers 
pressure  and  the  fracturing,  because  if  the  fracturing  occurs  too  early 
in  the  process  insufficient  pressure  may  be  exerted. 

There  are  many  coal  seams  which  contain  an  abundance  of  gas 

1  Campbell,  M.  R.,  Hypothesis  to  account  for  the  transformation  of  vegetable  matter 
into  the  different  grades  of  coal.  Econ.  Geology,  Vol.  I,  p.  26,  1905. 


170  THE  ORIGIN  OF   COAL 

which  escapes  by  blowers  or  by  oozing  out  during  the  mining  oper- 
ations. This  coal  is  not  necessarily  lower  in  fixed  carbon  than  other 
coal  which  does  not  give  off  so  much  gas  during  mining,  because  it 
has  absorbed  the  gas  in  its  pores.  If  the  pressure  be  sufficiently  great, 
the  gas  will  be  compressed  and  will  remain  in  the  coal,  but  in  all 
cases  where  it  cannot  escape  an  equilibrium  will  be  established  be- 
tween the  volatile  constituents  attempting  to  escape  and  the  com- 
pressed gas  already  given  off.  It  is  evident,  however,  that  other 
conditions  being  equal  less  pressure  will  be  required  to  raise  the  coal 
to  a  higher  type  if  the  gas  can  escape. 

7.  Effect  of  pressure.  —  Although  there  may  appear  to  be  many 
exceptions  to  the  rule  it  must  be  generally  recognized  that  anthracite 
and  other  high-carbon  coals  are  characteristically  found  in  regions  of 
crustal  disturbance  the  world  over.  Anyone  reading  the  descriptions 
of  coal  fields  will  find  that  if  any  country  contains  anthracite  it  is 
invariably  found  in  its  mountains  or  disturbed  areas,  and  this  con- 
dition goes  a  long  way  towards  establishing  the  thrust-pressure  hy- 
pothesis for  the  origin  of  anthracite.  This  hypothesis  has  in  recent 
years  been  worked  out  in  great  detail  by  White1  for  the  United  States, 
and  he  has  shown  that  this  is  the  most  logical  explanation  for  the 
devolatilization  of  coal  in  its  second  stage  of  development. 

There  are  certain  geological  factors  entering  into  a  consider- 
ation of  such  a  hypothesis  which  have  not  always  been  given  due 
consideration.  In  almost  any  coal  field  there  will  be  found  a  series 
of  sediments  made  up  of  heavy,  strong  beds,  such  as  sandstones  or 
conglomerates,  known  as  the  competent  beds;  and  others,  such  as 
coal  and  shale,  which  comprise  the  incompetent  beds.  When  pressure 
is  applied  to  these  strata  the  incompetent  beds  yield  and  adapt  them- 
selves to  the  movements  of  the  competent  beds  which  are  sufficiently 
strong  to  resist  buckling.  If  the  beds  always  lay  perfectly  horizontal, 
or  the  thrusts  were  always  applied  parallel  to  the  bed  and  equally  to 
all  the  competent  beds  there  would  be  no  important  result.  In  such 
a  heterogeneous  column  of  strata,  however,  there  are  oblique  thrusts 
and  therefore  movements  of  one  rock  over  another  in  various  direc- 
tions, with  the  result  that  great  pressures  are  exerted  on  the  coal  and 
the  shale  but  the  adjacent  competent  rocks  have  suffered  very  little 

1  White,  D.,  Op.  cit.,  p.  105;  and,  Some  problems  of  the  formation  of  coal.  Econ. 
Geol.,  Vol.  3,  p.  292,  1908. 


EFFECT  OF  PRESSURE  171 

deformation.  This  condition  is  well  illustrated  in  Figure  63,  where 
one  formation  is  highly  contorted  but  the  rocks  above  and  below  show 
no  effects  of  the  pressure.  Coal  acts  as  a  plastic  mass  in  the  early 
stages  of  its  development  from  vegetal  matter  as  illustrated  by  Figure 
74,  and  it  is  then  capable  of  accommodating  itself  to  almost  any 
shaped  space  without  showing  any  trace  of  the  movement.  These 
structural  principles  may  offer  an  explanation  of  the  flat-lying  an- 
thracite seams  in  the  Wyoming  basin  in  Pennsylvania  and  in  the  coal 
fields  of  China.  A  highly  fractured  stratum  is  not  always  evidence 
of  excessive  pressure  having  been  applied  in  that  area  but  it  is  evidence 
that  the  pressure  was  relieved.  It  may  not  have  done  more  than  a 
small  fraction  of  the  work  in  devolatilizing  the  coal  which  it  would 
have  done  had  it  been  applied  to  a  competent  bed  capable  of  with- 
standing that  pressure  and  of  transmitting  it  to  the  coal  seam.  A 
small  amount  of  heat  thus  generated  and  held  there  for  a  long  period 
of  time,  would  devolatilize  the  coal. 

If  this  principle  be  applied  to  the  well-known  anthracite  fields  of 
Pennsylvania  and  South  Wales  it  is  believed  that  it  will  explain  most 
of  the  features.  The  Pennsylvania  field  lies  in  a  highly  disturbed 
area  along  the  main  limb  of  the  anticlinorium  forming  the  Appal- 
achian Mountains  to  the  southeast  and  the  synclinorium  forming  the 
Appalachian  Valley  to  the  west  of  this  field.  There  is,  when  con- 
sidered on  its  broader  lines,  a  marked  difference  between  the  com- 
plicated structure  of  this  region  and  that  of  the  comparatively  simple 
structure  of  the  bituminous  field  farther  west.  It  is  probable  that 
this  area  suffered  an  unusual  amount  of  compression  where  the  mount- 
ains were  developed  and  the  fact  that  there  are  small,  comparatively 
undisturbed  areas  within  this  region  is  no  evidence  that  they  did 
not  suffer  from  intense  thrust  pressure.  The  thickness  of  the  whole 
series  of  strata  concerned  in  the  great  crustal  movements  must  have 
also  affected  the  pressure  exerted  on  the  coal  seams  although  the  seams 
lie  near  the  top  of  the  series.  The  strata  were  very  thick,  probably 
upwards  of  25,000  feet  in  that  region.  The  accompanying  map  of 
Pennsylvania  showing  the  fuel  ratios  of  the  coal  in  various  parts  of 
the  state  illustrates  the  relation  between  the  anthracite  and  bitu- 
minous areas  and  shows  the  gradation  from  one  to  the  other  (Fig. 
35)- 

Turning  to  the  South  Wales  anthracite  field,  so  well  described  by 


172 


THE   ORIGIN  OF   COAL 


EFFECT  OF  PRESSURE 


173 


o.^Z 


;u_z 


Strahan  and  Pollard,1  a  gradual  change  from  anT 
thracite  to  bituminous  coal  is  found,  but  with 
the  peculiar  condition  that  there  is  a  marked 
increase  in  the  ash  in  the  latter,  a  condition 
which  would  not  be  expected  if  part  of  the  bi- 
tuminous coal  gave  rise  to  anthracite  by  de- 
volatilization.  The  ash  content  as  indicated  by 
all  analyses  available  varies  from  about  i  per 
cent  at  the  anthracite  end  to  6  per  cent  at  the 
bituminous  end.  (Fig.  36.)  Various  explana- 
tions have  been  offered  to  explain  this,  such  as 
differences  in  the  original  vegetation  and  differ- 
ences in  the  extent  of  decomposition  before 
burial  of  the  vegetation.  These  are  not  satis- 
factory because  there  is  no  evidence  that  the 
vegetation  in  these  areas  was  different  and  if 
it  were  it  would  require  that  practically  all  the 
coal  in  the  bituminous  area  be  derived  from 
Equisetum  or  some  such  plant  to  give  rise  to  so 
much  ash.  If  the  same  plants  underwent  diff- 
erent degrees  of  decomposition,  this  would  tend 
toward  higher  carbonization  and  therefore  an- 
thracitization  but  it  certainly  would  not  reduce 
the  relative  ash  content  in  the  anthracite.  It 
would  appear  that  the  only  explanation  is  found 
in  the  addition  of  more  mineral  matter  to  the 
vegetation  while  it  was  accumulating,  or  later 
by  action  of  ground  water  percolating  through 
the  rocks. 

It  has  been  clearly  shown  that  the  anthra- 
citization  was  not  the  result  of  igneous  intru- 
sions, nor  does  there  seem  in  all  parts  of  the 
field  to  be  any  relation  between  the  lines  of 
iso-anthracitization,  and  the  original  outline  of 
the  basin  in  which  the  coal  was  deposited,  or  the 
present  outline  of  the  basin.  Strahan  and  Poll- 
ard have  shown  that  there  is  with  few  excep- 

1  Strahan,  A.,  and  Pollard,  W.,  Op.  cit.,  p.  80. 


174  THE   ORIGIN  OF   COAL 

tions  a  regular  increase  in  anthracitization  with  depth  and  also  in  going 
westward  from  the  eastern  border  of  the  basin,  but  they  conclude  that 
there  is  for  them  no  satisfactory  explanation  for  the  origin  of  the  an- 
thracite. Differences  in  original  vegetation  are  not  satisfactory;  nor  is 
the  metamorphism  by  pressure  hypothesis  substantiated  as  the  iso-an- 
thracitic  lines  do  not  correspond  with  the  lines  of  disturbance,  and 
the  faulting  which  has  so  profoundly  affected  the  region  was  later 
than  the  formation  of  the  anthracite  and  has  had  little  influence  on  it. 
Although  the  carbon-hydrogen  ratio  increases  with  depth  there  seems 
to  be  little  or  no  difference  between  the  coal  in  the  anticlines  and  that 
in  the  synclines. 

White  considers  that  the  isovols,  or  lines  of  equal  volatile  matter, 
in  this  field  follow  closely  lines  normal  to  the  thrusts  and  that  if  the 
area  were  worked  out  on  this  basis  the  thrust-pressure  hypothesis 
would  explain  the  anthracitization.  In  the  writer's  opinion  this  is 
the  only  explanation,  and  the  composite  chart  in  Figure  33  indicates 
that  the  iso-anthracitic  lines  follow  the  outlines  of  the  basin  except 
for  variations  which  would  be  the  logical  result  of  thrusting.  An 
example  of  this  may  be  seen  on  the  chart  in  the  Rhonda  No.  2 
vein. 

The  best  hypothesis  so  far  offered  for  the  origin  of  anthracite  and 
the  one  which  it  is  believed  will  explain  its  origin  in  all  the  fields  so 
far  studied,  if  logically  applied,  is  the  thrust-pressure  hypothesis. 

The  Origin  of  Cannel  and  Boghead 

As  early  as  1833  Hutton1  examined  cannel  coal  under  the  micro- 
scope and  found  small  "  cells  "  which  he  said  were  of  a  resinous 
nature  and  contained  a  wine-yellow  "  liquid."  This  seems  to  have 
been  the  first  time  that  the  spores  of  cannel  coal  had  been  noticed. 
Balfour,  Huxley,  Dawson,  Bertrand,  Renault,  and  Jeffrey  have 
since  that  time,  in  turn,  studied  these  spores  in  detail  and  added  much 
to  our  knowledge  concerning  them.  There  is  now  no  doubt  but  that 
cannel  consists  almost  entirely  of  spores  and  spore  exines  with  some 
of  the  other  more  resistant  portions  of  the  vegetal  matter.  These 
bodies  collect  in  open  water  and  form  layers  usually  of  lens-shape, 
in  the  other  types  of  coal. 

1  Hutton,  W.  Observations  on  coal.  London  and  Edinburgh  Phil.  Mag.  and  Jour, 
of  Sci.,  Vol.  II,  p.  302,  1833. 


THE   ORIGIN  OF  CANNEL  AND   BOGHEAD 


175 


Cannel  bears  certain  resemblances  to  the  bogheads,  including  the 
varieties  Torbanite,  oil  shales,  kerosene  shales,  and  bituminous  schists. 
There  seems  to  be  little 
doubt  that  the  organic 
matter  of  the  latter 
rocks  is  a  step  nearer 
petroleum  and  natural 
gas  than  that  of  the  or- 
dinary coals  and  in  this 
way  petroleum  is  related 
to  all  coals  through  these 
types  high  in  volatile 
constituents,  especially 
the  lighter  hydrocar- 
bons, and  lower  in  the 
carbohydrates.  The  best 
known  deposits  of  these 
rocks  are  the  Torbanite 
of  Scotland,  the  bitu- 
minous schists  of  Autun, 
France,  and  the  kerosene 
shale  of  New  South 
Wales,  Australia. 

Largely  as  a  result  of 
the  work  of  C.  E.  Bert- 
rand  and  B.  Renault1  it 
became  generally  accep- 
ted that  these  bogheads 
were  formed  from  gela- 
tinous algae.  The  rocks 
were  studied  micro- 
scopically and  certain 


FIG.  37.  —  (a)  Horizontal  section  through  the  bog- 
head of  Autun  showing  Pila  bibractensis  (x  17),  (6) 
Vertical  section  of  same  (x  38).  (After  C.  E.  Bert- 
rand.) 


minute   bodies   were   recognized   as   the   thalli   of  algae   (Fig.    37). 

1  Renault,  B.,  and  Bertrand,  C.  E.,  Note  sur  la  formation  schisteuse  et  le  boghead 
d' Autun.  Bull.  Soc.  1'industrie  minerale,  Tome  7,  3me  Ser.,  p.  499,  1893.  Also,  Pila 
bibractensis  et  le  boghead  d'Autun.  Soc.  d'Histoire  Naturelle  d'Autun,  Bull.  5,  p.  159, 
1892.  Also,  Reinchia  Australis  et  Premieres  Remarques  sur  le  Kerosene  Shale  de  la 
Nouvelle-Galles  du  Sud.  Soc.  d'Histoire  Naturelle  d'Autun,  Bull.  6,  p.  321,  1893. 


176  THE  ORIGIN  OF  COAL 

Bertrand1  describes  the  algae  as  occurring  as  a  hollow,  compressed 
sack  lying  in  a  brown  jelly,  which  is  known  as  the  fundamental  jelly 
and  which  is  said  to  carry  many  bacterial  bodies.  Between  the 
thalli  there  are  spores  and  grains  of  pollen  forming  thin  laminae  of 
orange  or  reddish-brown  color.  It  is  stated  that  the  algae  carry 
solid  material  to  the  extent  of  0.015  to  0.030  of  their  volume. 

Various  names  were  applied  to  the  supposed  algae  from  different 
regions.  Those  from  the  boghead  of  Autun  were  known  as  Pila 
bibractensis  and  those  from  the  kerosene  shale  of  New  South  Wales 
as  Reinschia  australis.  As  Thiessen2  has  pointed  out,  however,  there 
are  many  unsatisfactory  features  in  Bertrand's  explanation  of  the 
source  of  the  bituminous  matter  which  formed  the  fundamental  jelly. 
Jeffrey3  has  attacked  the  works  of  Renault  and  Bertrand  and  has 
shown  by  means  of  modern  section-making  methods  that  these  sup- 
posed algae  are  not  thalli  of  algae  but  spores  of  vascular  cryptogams. 
The  openings  in  the  supposed  thalli  are  the  tri-radiate  lines  on  the 
spores.  He  explains  the  difference  between  cannel  coals  and  boghead 
as  due  to  the  fact  that  the  latter  are  composed  of  larger  spores  than 
the  cannels,  i.e.,  they  consist  chiefly  of  macrospores.  The  fact  that 
oil  shales  derive  their  oils  and  gases  from  spores  has  been  verified  by 
other  investigators. 

Jeffrey's  conclusions  have  been  generally  accepted  but  one  writer 
claims  that  he  has  obtained  very  strong  evidence  in  support  of  the 
algal  theory  in  some  recent  deposits  in  Russian  lakes.  M.  D.  Zalessky4 
states  that  he  was  inclined  to  agree  with  Jeffrey  until  he  saw  well 
preserved,  silicified  specimens  of  Pila  from  Autun  and  he  has  recently 
examined  algal  deposits  which  are  now  forming.  In  the  brackish, 
shallow  lake,  Ala-Kool  which  lies  at  the  southern  extremity  of  the 
fresh- water  lake  known  as  Balkhash  and  which  is  overgrown  with 
aquatic  plants  there  lives  the  oleaginous  alga,  Botryococcus  braunii 

1  Bertrand,  C.  E.,  Charbons  gelosique  et  charbons  humique.     Compte  Rendu  VIII, 
Congres  Geologique  International,  p.  458,  1900. 

2  White,  D.,  and  Thiessen,  R.,  The  origin  of  coal.     U.  S.  Bureau  of  Mines,  Bull.  38, 
pp.  198-199,  1913- 

3  Jeffrey,  E.  C.,  The  nature  of  some  supposed  algal  coals.     Proc.  Amer.  Acad.  Arts 
and  Sciences,  Vol.  XL VI,  p.  273,  1910. 

4  Zalessky,  M.  D.,  On  the  nature  of  pila,  the  yellow  bodies  of  boghead  and  on  sapropel 
of  the  Ala-Kool  Gulf  of  Lake  Balkhash;    Extrait  du  tome  XXXIII  des  Bulletins  du 
Comite"  Geologique,  St.  Petersburgh,  No.  248,  1914. 


EFFECT  OF  PRESSURE  177 

in  such  superabundance  that  it  would  appear  that  sapropel  might 
form  from  it  on  the  lake  bottom  as  in  the  case  of  the  bogheads  in 
Permian  and  Carboniferous  time.  The  plankton  algae  come  to  the 
surface  and  they  have  been  analysed  by  S.  L.  Ivanov,  who  obtained 
the  following:  Oil,  3.5  per  cent;  number  of  free  fatty  acids,  12; 
ether  number  16;  saponification  number  28;  iodine  number  55.4. 
The  sapropelic  crust  formed  along  the  edge  of  the  lake  was  also  ana- 
lyzed and  with  ether  yielded  25  per  cent  of  its  substance.  The  ether 
was  then  evaporated  and  a  hard,  wax-like  mass  remained.  This 
mass  gave  acid  number  93.5  per  cent;  ether  number  46.7;  saponi- 
fication number  140.2;  iodine  number  31.5;  nitrogen,  0.4003  per  cent. 
Oleinic  acid  was  believed  to  be  present. 

A  hydrogen  sulphide  fermentation  takes  place  in  the  mass  and  when 
it  is  exposed  to  the  air  it  changes  from  a  green,  movable  body  into  a 
yellow-brown  solid,  elastic  and  reminding  one  of  a  mass  of  rubber, 
which  can  be  cut  with  a  knife.  Thin  sections  show  some  preserved 
cellular  structure  of  algae,  the  cavities  of  the  swollen  cells  being 
represented  by  roundish  pores.  Zalessky  claims  that  these  are  very 
similar  to  the  structures  seen  in  the  silicified  bogheads  of  Autun 
prepared  as  suggested  by  Jeffrey  and  he  considers  that  Pila  and 
Botryococcus  are  strikingly  alike.  The  mud  of  Ala-Kool  consists 
almost  exclusively  of  algae  of  this  type  with  a  few  other  green  algae 
and  some  diatoms. 

The  liquid  product  of  B.  brunni  reminds  one  of  tar  with  a  slight 
benzine  smell.  There  are  solids  like  vaseline  and  other  lubricants, 
and  since  Engler  obtained  artificial  petroleum  from  oleaginous  algae 
there  would  appear  to  be  a  possible  source  of  petroleum  in  this  type 
of  plant. 

These  observations  of  Zalessky  are  very  interesting  as  throwing 
new  light  on  this  subject,  but  it  is  doubtful  whether  he  will  con- 
vince most  observers  that  algae  were  the  source  of  the  bogheads. 
It  is  peculiar  that  if  these  algae  were  so  abundant  during  the  for- 
mation of  the  coal  measures  they  have  not  been  more  frequently 
recognized  in  coal  deposits,  while  on  the  other  hand  it  might  naturally 
be  expected  that  in  the  open  waters  of  almost  every  swamp  a  con- 
siderable amount  of  such  plant  material  should  be  laid  down. 


CHAPTER  VII 

FOSSIL  FLORA   OF  THE   COAL-FORMING   PERIODS 

Introduction 

Plants  are  the  source  of  all  coal  and  therefore  the  types  which 
formed  it  and  their  distribution  are  matters  of  vital  interest  to  all 
who  study  the  origin  of  coal  deposits.  The  climatic  conditions 
existing  during  the  coal-forming  periods  and  the  question  as  to  whether 
the  plants  of  those  periods  were  similar  to  those  now  living  on  the 
earth  are  also  subjects  for  special  consideration.  The  fossil  plants 
are  our  best  geologic  thermometers  and  hygrometers  and  we  are  largely 
dependent  upon  them  for  our  information  regarding  the  earth's 
early  climates. 

In  searching  for  plant  fossils  one  seldom  finds  distinct  forms  in 
the  higher  grade  coal  itself  unless  they  are  enclosed  in  "  coal  balls  " 
where  they  are  almost  hermetically  sealed.  The  soft,  semi-plastic 
vegetal  matter  which  forms  the  coal  is  partially  destroyed  by  bac- 
terial action  and  oxidation  and  then  is  squeezed  so  that  little  sign 
of  the  original  plants  remains  evident  to  the  naked  eye  except  that 
in  some  cases  a  large  fragment  of  a  tree  trunk  may  resist  complete 
destruction.  In  the  coal  balls  the  most  delicate  plant  structures 
may  be  preserved  and  aside  from  them  the  best  fossils  occur  in  the 
shales  and  slates  of  the  partings  or  in  the  roof  or  floor  of  the  seam. 
Delicate  structures  are  sometimes  preserved  in  these  rocks,  which, 
being  originally  muds,  have  formed  good  coverings  for  the  plants  as 
they  have  sealed  them  very  tightly.  In  the  coarser  sandstones  and 
conglomerates  only  casts  of  the  larger  fragments  of  plants  are  pre- 
served, due  to  two  reasons,  one  the  ready  access  of  air  and  water  to 
the  plant  fragment,  causing  it  to  decay  without  leaving  a  good  im- 
print, and  the  other  the  coarseness  of  the  material  surrounding  the 
plant.  This  prevents  the  various  particles  of  the  plant  from  being 
held  in  their  proper  position  for  the  production  of  perfect  impressions 
of  its  structure. 

A  study  of  fossil  plants  satisfies  us  that,  in  many  respects,  the 

178 


INTRODUCTION 


179 


vegetation  existing  during  the  coal-forming  periods  was  similar  to 
that  now  found  upon  the  globe.  The  changes  from  the  earliest 
land  vegetation  to  the  modern  types  have,  on  the  whole,  been  gradual 
although  a  few  sudden  and  marked  changes  have  occurred.  The 
first  great  development  of  land  plants,  which  made  the  formation  of 
coal  possible,  occurred  in  the  Devonian  period,  and  from  Upper  Dev- 
onian time  until  the  Pleistocene  there  was  not  a  period  in  the  earth's 


FIG.  38.  —  Lepidodendron  lycopodivides,  (Sternberg)  showing  branches 
and  leaves.     (After  Zeiller.) 

history  when  coal  was  not  fo  ming  somewhere  on  the  earth.  This 
indicates  that  the  formation  or  non-formation  of  coal  during  any  period 
since  the  first  appearance  of  land  plants  has  been  fundamentally  de- 
pendent upon  the  topographic  and  climatic  conditions  then  existing 
on  the  globe  rather  than  on  the  lack  of  plants  or  of  any  particular 
kind  of  plant.  There  seems  always  to  have  been  a  flora  ready  to 


l8o  FOSSIL  FLORA  OF  THE  COAL-FORMING   PERIODS 

populate  any  region  where  conditions  were  suitable  for  development. 
Everything  points  to  the  fact  that  it  matters  little  what  kind  of  plant 
enters  into  the  constitution  of  coal,  but  the  physical  and  chemical 
changes  which  the  vegetation  later  undergoes  produce  the  profound 
differences  in  the  different  types  of  coal  derived  from  it. 

The  Rise  of  the  Land  Plants 

The  two  outstanding  features  in  the  evolution  of  the  earth's 
vegetation  are  the  great  development  of  the  Pteridophytes,  known 
to  many  as  the  Vascular  Cryptogams,  in  the  early  days  of  land  plants, 
and  the  advent  of  the  flowering  plants  comparatively  late  in  the 
earth's  history. 

The  Pteridophytes  include  the  Filicales,  or  ferns;  the  Equise- 
tales,  or  horsetails;  the  Lycopodiales,  or  lycopods,  and  the  Spheno- 
phy Hales.  All  of  these  were  present  in  the  Devonian  and  they  reached 
an  extraordinary  degree  of  perfection  in  the  Carboniferous.  The 
ferns  have  continued  to  flourish  through  all  the  periods  to  the  present 
day,  with  the  disappearance  of  many  genera  and  the  appearance  of 
new  ones.  The  horsetails  had  representatives  in  the  Carboniferous 
which  were  good-sized  trees,  and  they  continued  as  such  until  the 
end  of  the  Jurassic  when  the  last  great  trees  of  this  type  disappeared 
and  the  group  degenerated  until  it  is  now  represented  only  by  the 
insignificant  Equisetum. 

The  lycopods  of  the  genera,  Lepidodendron  and  Sigillaria  formed 
giant  trees  which  were  dominant  in  many  of  the  coal  basins.  They 
disappeared  very  early  in  the  history  of  land  plants,  Lepidodendron 
not  even  reaching  the  Permian  and  only  a  few  species  of  Sigillaria 
existing  in  the  lower  portion  of  that  system.  For  the  sudden  ending 
of  these  great  genera  in  the  Northern  Hemisphere  there  is  not  much 
explanation  because  there  seems  to  be  little  evidence  of  a  sudden 
change  in  climate,  although  the  prevalence  of  red  beds  and  the  pres- 
ence of  annual  rings  of  growth  in  trees  indicate  approaching  aridity 
and  more  distinctly  marked  seasons.  In  the  Southern  Hemisphere 
their  extinction  is  more  readily  understood  as  it  corresponds  closely 
with  the  inception  of  glacial  conditions  which  practically  wiped  out  the 
previously  existing  flora  and  introduced  the  Gangamopteris  flora 
containing,  as  common  forms,  Gangamopteris,  Glossopteris  and 
Rhacopteris.  The  latter  flora  has  been  an  accompaniment  of  inter- 


THE   RISE  OF  THE  LAND   PLANTS 
PLATE  V. 


181 


A  group  of  grains,  cones,  spores,  and  seeds  from  the  Coal  Measures  of  France. 
Figs,  i,  2,  Male  floral  organs  of  cordaites;  Fig.  3,  Grains  of  pollen;  Figs.  4,  5,  6, 
7,  Cordaianthus  gemmifer;  Figs.  8,  9,  10,  n,  12,  13,  14,  15,  Cordaianthus  bacci- 
fer;  Figs.  16,  17,  18,  Cordaicarpus  major,  ventricosus,  vellavus;  Figs.  19,  20,  21, 
C.  Guthbieri,  ovatus,  congruens;  Fig.  22,  Cordaicarpus  punctatus,  Gr.;  Figs.  23, 
24,  25,  C.  drupacens,  expansus,  reniformis;  Fig.  26,  C.  eximius;  Fig.  27,  Diplotesta 
Grand'Euryana  (Brong.);  Fig.  28,  Carpolithes  avellanus.  (After  Grand'Eury.) 


182  FOSSIL   FLORA  OF  THE   COAL-FORMING  PERIODS 

glacial  periods  in  Australia,  India,  South  Africa,  and  South  America. 
All  of  these  countries  were  more  or  less  closely  linked  up  in  the  Per- 
mo-Carboniferous  by  land  connections.  This  flora  has  also  been  found 
to  a  limited  extent  in  the  Northern  Hemisphere  as,  for  example,  in 
European  Russia  which  could  be  easily  reached  from  India  since  the 
Himalaya  Mountains  were  not  then  in  existence. 

This  change  in  the  vegetation  of  the  Southern  and  to  a  lesser 
extent  in  that  of  the  Northern  Hemisphere  is  the  most  sudden  change 
in  the  history  of  plant  life  on  the  earth.  In  the  coal  fields  of  America 
there  was  a  great  change  in  the  vegetation  during  the  Permian,  as 
every  species,  but  not  every  genus,  of  the  Coal  Measure  plants  dis- 
appeared early  in  that  period.  The  increasing  dryness  and  the  ele- 
vation of  the  Appalachian  Mountain  system  had  a  profound  influence 
on  the  flora  of  the  eastern  part  of  the  continent,  which  was  the  only 
great  land  area  at  that  time  as  most  of  the  western  portion  of  the 
continent  was  under  the  sea.  Many  genera  and  some  families  ceased 
to  exist,  and  when  the  Triassic  period  opened  the  Gymnosperms 
had  become  the  dominant  type  of  vegetation  in  place  of  the  Pteri- 
dophytes,  or  Vascular  Cryptogams. 

The  Gymnosperms,  or  "  naked-seed  "  plants  were  represented  in 
the  Devonian  by  the  Cycadofilicales,  a  group  of  seed  plants  which 
strongly  resembled  some  of  the  ferns  in  appearance  but  which  bore 
seeds  and  were  similar  to  the  cycads  in  some  other  respects.  These 
plants  occupied  a  very  prominent  position  in  the  Carboniferous  period 
and  were  for  a  long  time  mistaken  for  ferns.  The  Gymnosperms 
were  also  represented  by  the  conifers  which  appeared  in  the  Devonian 
and  which  left  some  traces  in  the  Carboniferous.  In  the  Permian, 
Walchia  and  Voltzia  were  typical  examples  of  this  group,  which  be- 
came much  more  prominent  in  the  Triassic  than  it  had  been  previously. 
During  the  Jurassic  some  of  our  more  modern  types  of  conifers,  like 
the  pine  and  the  cypress,  appeared  and  continued  to  flourish. 

Another  great  Gymnosperm  group  was  the  Cordaitales  which 
appeared  in  the  latter  part  of  the  Devonian  period,  became  very 
abundant  in  the  Carboniferous  and  gradually  died  out  before  the 
close  of  the  Paleozoic.  These  plants  were  probably  the  ancestors  of 
the  Gingkoales.  The  latter  became  abundant  in  the  middle  of  the 
Mesozoic  era  and  then  gradually  declined  until  the  group  is  now 
represented  by  the  single  species,  Gingko  biloba.  The  cycads  were 


THE   RISE  OF  THE   LAND   PLANTS 


183 


PLATE  VI. 


Lepidodendron  aculeatum  (Sternberg)  showing  the  leaf  scars  and  the  varying  ap- 
pearance of  these  when  portions  of  the  bark  are  removed,  i  A  is  an  enlargement  of 
one  of  the  leaf  cushions,  and  7  illustrates  the  bark  of  an  old  tree.  (After  Zeiller.) 


184  FOSSIL  FLORA   OF  THE   COAL-FORMING  PERIODS 

represented  in  the  Coal  Measures  and  they  gradually  developed  to  a 
climax  in  the  Jurassic.  They  have  since  declined  in  relative  im- 
portance. 

From  the  Triassic,  which  seems  to  have  marked  the  beginning  of 
the  dominance  of  the  more  modern  vegetation  over  that  of  the  Pale- 
ozoic, the  flora  has  become  more  and  more  like  that  with  which  we 
are  now  familiar.  There  were  periods  of  adversity  for  the  plants 
and  there  were  periods  like  the  Jurassic  and  early  Tertiary  when  the 
climate  seems  to  have  been  fairly  uniform  from  the  equator  to  the 
poles.  During  these  periods  the  tropical  and  subtropical  species 
spread  far  to  the  north  and  south  as  they  did  in  the  Carboniferous, 
and  the  remains  of  plants  like  the  cycads,  which  we  now  think  of  as 
tropical  and  subtropical  lie  beneath  the  Arctic  snows. 

In  the  Triassic1  the  Gymnosperms  were  dominant  but  the  flora 
on  the  whole  was  not  luxuriant  as  in  the  Carboniferous.  The  horse- 
tails were  large  and  abundant.  There  were  many  ferns  and  conifers. 
The  cycads  were  beginning  to  be  numerous. 

The  Jurassic  period  showed  a  much  greater  development  of  modern 
genera  than  did  any  previous  period.  The  cycads  reached  their 
climax  and  the  period  has  been  called  the  "  Age  of  Cycads."  Mod- 
ern conifers  like  pines,  arbor  vitae,  and  cypresses  appeared. 

With  the  opening  of  the  Lower  Cretaceous,  or  the  Comanchean  of 
America,  an  important  event  in  the  evo  ution  of  plants  occurred. 
This  was  the  appearance  of  the  Angiosperms,  or  "  enclosed-seed  " 
plants.  These  flowering  plants,  apparently  originating  in  the  north- 
eastern part  of  the  continent,  soon  spread  all  over  it,  and  many  modern 
genera  of  eucalypti,  figs,  magnolias,  cinnamon,  and  others  well  known 
today,  made  their  appearance  and  have  contrived  to  flourish  to  the 
present  time.  In  the  Upper  Cretaceous  the  beech,  birch,  oak,  wal- 
nut, breadfruit,  and  holly  were  all  present  and  the  flora  had  assumed 
quite  a  modern  aspect. 

Classification  of  Plan 

In  a  classification  of  plants  which  includes  foss'l  types  it  should  be 
pointed  out  that  the  fossil  plants  must  be  divided  into  genera  which 
are  founded  on  a  basis  different  from  that  used  in  a  classification  of 

1  Fontaine,  W.  M.,  Older  Mesozoic  flora  of  Virginia.  U.  S.  Geol.  Survey,  Monograph 
VI,  1883. 


CLASSIFICATION  OF  PLANTS 


185 


living  plants.  This  is  owing  to  the  incompleteness  of  the  fossils 
since  parts  of  the  plant  may  be  separated  from  each  other  or  entirely 
destroyed.  It  is  necessary  to  classify  them  into  what  may  be  called 
"  form  "  genera,  based  on  the  form  of  the  fragment.  For  example, 
the  genus  Lepidodendron  includes  the  stem  of  a  tree  and  Stigmaria 
the  root  of  the  same  tree.  Such  an  arrangement  of  genera  is  not 
found  in  the  classification  of  living  plants. 


•rt 


FIG.  39.  —  Group  of  grains  representing  the  seeds  of  various  plants  in  the  Coal  Meas- 
ures of  France  A,  B,  Trigonocarpus  (Brong.);  C,  Polylophospermum  (Brong.);  D,  E,  F, 
Polypterocarpus;  G,  H,  Codonospermum  (Brong.);  I,  Carpolithes  sulcatus  (Prest.); 
J,  K,  L,  M,  Rhabdocarpus  (Gopp  and  Berg).  (After  F.  C.  Grand'Eury,  Flore  Carbon- 
ifere  du  Departement  de  la  Loire.) 

Many  botanists  have  divided  all  plants  into  two  large  groups,  the 
Cryptogams  or  spore-bearing  plants,  and  the  Phanerogams,  or  flower- 
ing plants.  The  former  supposedly  included  all  those  in  which  the 
sexual  reproduction  is  concealed,  thus  embracing  all  the  lower  types. 
In  the  Phanerogams  the  reproduction  was  thought  to  be  exposed  in 
the  stamens  and  pistils  which  were  mistaken  for  sexual  organs.  In 
this  division  were  placed  all  the  seed  plants. 

In  more  recent  classifications,  however,  the  seed  plants  are  known 
as  Spermatophytes  and  they  are  divided  into  the  Gymnosperms  and 
Angiosperms,  the  former  comprising  the  primitive  seed  types  and 
the  latter  the  more  highly  developed  and  more  modern  flowering 
plants.  As  might  be  expected,  the  older  fossil  seed  plants  all  belong 


186  FOSSIL   FLORA  OF  THE   COAL-FORMING  PERIODS 

to  the  Gymnosperm  group  as  do  also  many  of  the  later  fossils,  and  our 
discussion  of  the  coal  flora  will  be  confined  largely  to  a  discussion 
of  this  group,  as  the  Angiosperms  did  not  appear  on  the  earth,  so 
far  as  known,  before  the  Cretaceous  period.  In  a  modern  classi- 
fication1 of  plants  the  following  divisions  are  recognized:  (i)  Thal- 
lophytes, (2)  Bryophytes,  (3)  Pteridophytes,  and  (4)  Spermatophytes. 

(i)   THE  THALLOPHYTES 

The  Thallophytes  are  plants  of  the  simplest  form  and  they  get 
their  name  from  the  fact  that  with  few  exceptions  they  consist  only 
of  thalli.  The  thallus  is  an  undifferentiated  vegetal  body  which  in 
its  lowest  form,  like  the  animal  amoeba,  does  not  have  a  division  of 
functions.  In  such  forms  the  jelly-like  mass  of  protoplasm  can  push 
out  legs,  or  pseudopodia  for  purposes  of  locomotion  and  these  may 
surround  particles  of  food  which  become  engulfed  in  the  mass  and  are 
absorbed.  The  processes  of  reproduction  are  simple.  In  some 
cases  there  is  simple  division,  in  others  a  spore  is  produced  which 
gives  rise  to  the  new  plant.  Some  of  the  higher  forms  possess  multi- 
cellular  sex  organs. 

There  are  two  important  divisions  of  the  Thallophytes  including 
(i)  Algae  and  (2)  Fungi.  The  Algae  are  subdivided  according  to 
color  into  the  "  Blue-Green,"  the  "  Green,"  the  "  Brown  "  and  the 
"  Red  "  Algae. 

The  Fungi  are  subdivided  into  at  least  four  groups  which  contain 
respectively,  the  water  moulds  and  the  mildews;  rusts  and  smuts; 
the  toadstools,  mushrooms  and  puffballs;  the  bacteria  and  the  lichens. 

The  Algae  vary  in  size  from  microscopic  organisms  to  the  large 
seaweeds,  and  many  of  the  Fungi  are  so  minute  that  they  cannot  be 
seen  with  the  naked  eye. 

From  a  palaeontological  standpoint  the  Algae  existed  in  pre- 
Cambrian  time  and  they  have  been  abundant  in  certain  geological 
periods,  although  it  is  doubted  whether  they  played  any  important 
part  in  the  formation  of  coal.  Bacteria  have  also  been  in  existence 
since  early  geological  time  and  their  influence  in  coal  formation  has 
been  discussed  in  connection  with  the  biochemical  processes  in  the 
origin  of  coal.  It  is  believed  that  fungi  such  as  mushrooms  have  also 

1  Coulter.  J.  M.,  Barnes,  C.  R.,  and  Cowles,  H.  C.  A  textbook  of  botany,  Vol.  I, 
1910 


CLASSIFICATION   OF  PLANTS 


I87 


PLATE  VII. 


i  —  4,  Sigillaria  elegans  (Sternberg);  5  — 10,  Sigillaria  mamillaris  (Brongniart). 
These  figures  illustrate  the  different  appearance  of  the  specimens  when  portions  of 
the  bark  have  been  removed,  i  and  5  show  the  scars  of  the  organs  of  fructification 
as  well  as  the  leaf  scars;  4  and  6  show  the  posterior  side  of  the  bark;  10  is  from  a  young 
tree.  (After  Zeiller.) 


l88  FOSSIL   FLORA  OF  THE   COAL-FORMING  PERIODS 

been  instrumental  in  producing  biochemical  changes  in  peat  as  far 
back  as  the  Carboniferous  period.  Any  evidence  of  fossil  Thallo- 
phytes, so  far  as  known,  can  be  seen  only  by  aid  of  the  microscope  and 
therefore  these  plants  do  not  concern  the  average  person  collecting 
plant  fossils. 

(2)  THE  BRYOPHYTES 

The  Bryophytes  are  a  large  group  of  plants  showing  a  distinct 
advance  over  the  Thallophytes  in  structure.  They  show  a  definite 
alternation  of  generations  and  are  characterized  by  sexual  and  sexless 
individuals.  The  gametophyte  produces  the  sex  organs  and  the 
sporophyte  produces  the  spores.  The  members  of  the  group  possess 
an  archegonium  which  is  characteristic  of  higher  plants,  and  they  thus 
show  their  relation  to  these  higher  forms.  They  possess  a  multi- 
cellular  antheridium  much  more  highly  developed  than  that  of  the 
Thallophytes. 

This  group  is  divided  into  two  main  divisions  (i)  Hepaticae  or 
liverworts  and  (2)  Musci,  or  mosses,  including  the  Sphagnales  or 
"  bog  mosses  ";  the  Andreaeales;  and  the  Bryales,  or  "  true  mosses." 
The  Bryophytes,  or  Bryinae  are  regarded  by  Land  and  others  as  of 
recent  origin  although  it  has  been  claimed  that  barren  forms  of  this 
group  have  been  found  in  the  Carboniferous  of  France.  They  are  of 
little  interest  from  the  palaeontological  standpoint  but  the  Sphag- 
nales, comprising  the  genus  Sphagnum,  are  of  much  interest  at  the 
present  time  because  of  the  importance  of  this  genus  in  the  formation 
of  peat  in  the  cooler  climates. 

(3)  THE  PTERIDOPHYTES 

The  group  of  Pteridophytes  contains  many  important  fossil  species 
in  addition  to  numerous  well-known  living  forms,  such  as  ferns,  horse- 
tails and  club-mosses.  They  are  characterized  by  a  vascular  system, 
or  series  of  vessels  for  conducting  material  from  one  part  of  the  plant 
to  another,  and  from  this  character  they  are  frequently  known  as  the 
Vascular  Cryptogams.  This  vascular  system  serves  to  separate  the 
Pteridophytes  very  sharply  from  the  Bryophytes  and  Thallophytes, 
but  it  is  found  in  the  Spermatophytes  and  shows  the  relation  of  the 
Pteridophytes  to  these  higher  seed  plants.  The  gametophyte,  known 
as  the  prothallium,  and  the  sporophyte  are  independent  of  each  other. 


CLASSIFICATION  OF  PLANTS 


189 


The  pro  thallium  develops  from  a  spore  and  on  it  the  oo  spore  develops 
in  the  archegonium,  giving  rise  to  the  sporophyte,  the  full-fledged 


FIG.  40.  —  i  Sigillariostrobus  goldenbergi.  (O.  Feistmantel.) ;  2  S.  tieghemi  (Zeiller); 
4  S.  goldenbergi  (Zeiller);  i,  2,  2  A  and  4  show  cones  of  fructification;  2  B  and  4  A  are 
macrospores  enlarged.  (After  Zeiller.) 

plant,  bearing  spores  in  the  sporangia.  Most  people  are  familiar 
with  the  dark  spots  on  the  under  side  of  fern  leaves.  Each  of  these 
spots  is  a  group  of  sporangia  known  as  a  sorus.  It  is  considered  that 


FOSSIL  FLORA   OF  THE   COAL-FORMING  PERIODS 

the  Pteridophytes  have  been  developed  from  a  liverwort-like  an- 
cestor. 

This  group  has  been  subdivided  by  Coulter,  Barnes,  and  Cowles1 
into  six  groups  as  follows:  (i)  Lycopodiales  or  club-mosses,  (2) 
Psilotales,  (3)  Sphenophyllales,  including  only  the  fossil  genus  Spheno- 
phyllum,  (4)  Equisetales,  or  "  horsetails,"  (5)  Ophioglossales,  in- 
cluding the  common  adder's  tongue  and  moonwort,  and  (6)  Filicales, 
or  ferns,  including  the  Filicineae  or  "  true  ferns  "  (homos porous)  and 
Hydroteridineae,  or  "  water  ferns  "  (heteros porous). 

Zeiller2  makes  the  following  four  divisions  (i)  Filicineae,  or  ferns, 
(2)  Rhizocarpeae,  or  Hydropterides,  often  placed  as  a  sub-class  under 
the  Filicineae,  (3)  Equisetineae  and  (4)  Lycopodineae.  Of  these 
(i),  (3)  and  (4)  are  well  represented  among  the  Coal  Measure  fossils, 
but  (2)  is  absent  unless  Sphenophyllam  be  put  in  that  class  as  some 
have  placed  it,  although  it  is  more  nearly  related  to  the  Lycopodineae. 
It  has  no  living  representative. 

(1)  The  Lycopodiales.  —  There  are  several  living  and  many  ex- 
tinct genera  in  this  group.  Lycopodium,  which  is  the  best  known, 
has  been  characterized  by  Coulter  as  possibly  the  best  living  repre- 
sentative of  the  earliest  forms  of  vascular  plants.  Some  have  re- 
garded Phylloglossum,  an  Australian  species,  as  the  most  primitive 
Pteridophyte. 

In  Lycopodium  the  plant,  or  sporophyte,  is  a  branching  stem  cov- 
ered with  many  small  leaves  and  on  each  of  these  there  is  a  spo- 
rangium on  the  upper  side.  The  term  sporophyll  is  applied  to  these 
spore-bearing  leaves  and  when  grouped  together  they  form  a  strobilus. 
There  is  a  tendency  in  some  of  these  plants  for  the  lower  leaves  to  be- 
come sterile  and  cease  to  bear  sporangia,  while  this  function  is  carried 
on  entirely  by  stalk-like  sporophylls  rising  above  the  foliage  leaves. 

The  stem  shows  two  zones,  an  outer  one  of  cells  known  as  the  cor- 
tex and  an  inner  one  known  as  the  stele  in  which  the  vascular  system 
is  found.  From  the  vascular  cylinder,  strands  extend  through  the 
cortex  to  form  the  leaf  traces  on  the  exterior. 

The  Lycopodiales,  although  now  represented  only  by  the  humble 
club-mosses,  were  in  Carboniferous  time  among  the  large  trees  and 
their  fossil  forms  are  as  a  rule  arborescent. 

1  Op.  cit.,  p.  122. 

2  Zeiller,  R.,  Bassin  houiller  de  Valenciennes,  Description  de  la  Flore  Fossile,  Text 
and  Atlas.    Paris,  1888. 


THE  LYCOPODIALES 


IQI 


Two  well-known  families,  Lepidodendrae  and  Sigillariae,  are  found 
widely  distributed  in  later  Paleozoic  rocks.  Under  the  Lepidodendrae 
several  genera  have  been  recognized:  Lepidodendron  (Sternberg), 
Lepidopholios  (Sternberg),  Halonia  (Lindley  and  Button),  Bothro- 
dendron  (Lindley  and  Hutton),  Lepidostrobus  (Brongniart),  Lyco- 


FIG.  41.  —  i  Stigmaria  ficoides  (Brongniart)  showing  main  roots  and  attached  rootlets; 
2  and  3,  Scars  where  rootlets  have  been  attached.     (After  Lesquereaux,  Pa.  Geol.  Survey.) 

podites  (Brong.),  Lepidophyllum  (Brong.).     Of  these  Lepidodendron 
is  best  known  and  it  will  be  described  as  a  type. 

Lepidodendron  (Sternberg):  Plants  of  this  genus  formed  trees  in 
Paleozoic  time  which  according  to  Grand 'Eury1  reached  a  meter  in 
diameter  and  30  meters  in  height,  with  leaves  in  some  cases  a  meter 
long.  They  and  the  Sigillariae  are  so  abundant  in  the  Coal  Measures 
and  their  stems  are  so  characteristic  that  they  have  always  attracted 
a  great  deal  of  attention  among  miners  and  others  collecting  plant 
fossils.  Sigillaria  is  recognized  by  the  parallel  vertical  lines  of  leaf 

1  Grand'Eury,  F.  C,  Flora  carbonifere  du  Departement  de  la  Loire  et  du  Centre  de 
la  France;  Paris,  p.  148.  1877. 


1 92  FOSSIL  FLORA  OF  THE   COAL-FORMING  PERIODS 

cushions  on  the  bark  while  Lepidodendron  is  distinguished  from  it  by 
its  spirally  arranged  lines  of  leaf  scars. 

The  leaves  of  Lepidodendron  are  generally  acicular,  and  very  long 
on  the  stems,  but  much  shorter  on  the  branches;  they  diminish  in 
size  with  each  bifurcation  of  the  axis.  On  the  stem  they  are  attached 
to  elongated-rhomboidal  to  pointed-oval  cushions,  (Fig.  38).  When 
the  epidermis  is  present  these  cushions  show  three  bodies  making  up 
one  structure  roughly  oval  in  outline  and  sharply  tapering  at  one  end. 
The  other  end  is  capped  by  a  small  rhomb  with  three  small  dots. 
Above  this  rhomb,  close  to  the  end  of  the  cushion,  is  a  small  scar 
representing  the  leaf-detachment  scar.  The  small  dots  are  re- 
garded by  most  writers  as  leaf-bundle  traces,  although  some  think 
that  only  the  middle  one  is  of  this  origin.  If  the  outer  bark  be  re- 
moved, a  new  condition  is  presented  and  each  cushion  shows  only 
one  scar  at  the  top.  (Plate  VI.) 

The  cushions  are  in  contact  with  one  another  except  that  in  some 
specimens  they  are  separated  by  sharp  furrows  and  in  others  by  broad 
flat  strips.  According  to  Stur1  who  has  given  detailed  descriptions 
of  these  fossils,  the  former  are  older  plants  than  the  latter. 

As  to  the  reproduction  of  the  arborescent  fossil  Lycopods,  Zeiller2 
says  that  they  appear  to  have  been  heterosporous.  The  greater 
part  of  the  cones  of  fructification  in  which  the  structure  has  been 
studied  seem  to  carry  the  macrosporangia  on  the  lower  and  the  micro- 
sporangia  on  the  upper  bracts.  He  still  feels,  however,  that  the 
matter  has  not  been  fully  settled. 

Geologic  and  geographic  distribution:  .Lepidodendron  was  widely 
distributed  over  the  earth  in  Carboniferous  and  sub- Carboniferous 
time.  It  seems  to  have  been  found  in  every  country  where  coal  was 
forming  at  that  time,  reaching  its  maximum  development  in  the 
lower  and  middle  Coal  Measures  and  then  declining.  In  Australia 
no  trace  of  it  is  found  even  in  the  Permo-Carboniferous  deposits 
as  it  had  died  out  before  they  were  laid  down,  and  in  Europe  it  barely 
extends  into  the  Permian.  In  North  America  it  has  not  extended 

1  Stur,  D.,  Die  Culmflora  der  Ostrauer  und  Waldenburger  Schichten.  Abh.  d.  k.  k. 
Geol.  Reichsanstalt  zu  Wien,  Vol.  8,  Heft  II,  also  Die  Culmflora  des  mahrisch-schlesis- 
chen  Dachschiefers,  Heft  I,  1877.  Quoted  by  Solms-Laubach  in  Fossil  Botany,  Rev. 
Trans,  by  Balfour,  I.  B.,  1891. 

*  Zeiller,  R.,  Op.  cit. 


THE  LYCOPODIALES 


193 


into  the  Permian.1  It  is  confined,  therefore,  to  the  Paleozoic.  The 
earliest  appearance  of  the  genus  is  reported  to  be  in  the  Lower  Dev- 
onian beds  of  Wieda  and  Hartz.2  It  is  widely  distributed  in  America. 


FIG.  42. —  1-2  aa,  Annularia  longifolia  (Brongniart);  2  b,  2  bb,  A.  inflata  (Les- 
quereaux);  j,  30,  Asterophyllites  equisetiformis  (Brong.);  4-50,,  A.  gracilis  (Lesq.); 
6,  7,  Sphenophyllum  schlotherinne  (Brong.);  8,  9,  Annularia  sphenophylloides  (Zenk.); 
10,  loa,  Sphenophyllum  bifurcatum.  (After  Lesquereaux,  Pa.  Geol.  Survey). 

Europe,  and  Australia  in  the  Upper  Devonian  and  the  Mississippian, 
or  Sub-Carboniferous. 

Sigillariaea:  Under  the  family  Sigillariaea  have  been  described 
the  genera  Sigillaria  (Brongniart)3,  Sigillariostrobus  (Schimper),  and 
Stigmaria  (Brong.).  It  has  been  known,  however,  since  the  work 
of  Binney  that  Stigmaria  is  not  a  genus  but  simply  the  root  of 
Sigillaria  and  Lepidodendron. 

1  Solms-Laubach,  Fossil  botany.     Rev.  Trans,  by  Balfour,  I.  B.,  p.  194,  1891. 

2  Fontaine,  W.  M.,  and  White,  I.  C.,  Permian  flora.      2nd  Geol.  Survey  Pa.,  Pt.  PP, 
p.  114,  1880. 

8  Solms-Laubach,  Op.  cit 


194 


FOSSIL  FLORA  OF  THE   COAL-FORMING  PERIODS 


Of  the  others,  Sigillaria  (Brong.)1  is  by  far  the  best-known  genus. 
As  already  stated,  it  may  be  distinguished  from  Lepidodendron  by 
the  fact  that  the  leaf  scars  are  arranged  in  vertical,  parallel  bands 
rather  than  in  spirals.  Our  knowledge  of  the  leaves  and  many  other 
features  is  not  as  great  as  it  is  of  those  of  Lepidodendron. 


FIG.  43.  —  Calamites  suckowi  (Brongniart)  with  articulations  and  secondary  branches. 
Coal  Measures  of  France.     (After  Zeiller.) 

The  leaf  cushions  are  roughly  polygonal  in  outline  and  they  may 
be  compressed  vertically  so  as  to  give  a  transversely  elongated  six- 
sided  figure  with  the  two  horizontal  sides  considerably  longer  than 
the  other  four,  which  are  approximately  equal.  (Plate  VII.)  When 
of  this  form  they  are  compressed  together  so  that  they  form  vertical 
ribs  of  scars  alternating  in  adjacent  rows. 

Along  the  upper  side  of  the  cushion  there  are  three  small  marks. 
The  middle  is  punctiform  or  somewhat  elongated  transversely,  while 
the  others  are  short,  thin  marks  diverging  from  it.  These  marks 
represent  the  leaf  traces. 

1  Brongniart,  A.,  Observations  sur  la  structure  interieure  du  Sigillaria  elegans  com- 
pare"e  a  celle  des  Lepidodendron  et  des  Stigmaria  et  a  celle  des  vegetaux  vivants.  Ar- 
chives du  Museum  d'Hist.  Nat.  Vol.  I,  1839. 


THE   LYCOPODIALES 


195 


There  is  a  good  deal  of  uncertainty  about  the  leaves  of  Sigillaria, 
but  leaves  which  are  believed  to  be  from  these  trees  have  been  de- 
scribed by  a  number  of  botanists.  They  are  long  and  have  a  keel 
resulting  from  the  projection  of  the 
median  nerve.  White1  has  found 
leaves  in  the  Missouri  Coal  Meas- 
ures which  he  describes  as  probably 
belonging  to  Sigillaria.  They  were 
broad,  rather  thin,  but  seldom 
flattened.  Some  fragments  were 
20  cm.  long  and  5  to  n  cm.  in 
width.  They  tapered  very  grad- 
ually and,  from  the  appearance  of 
certain  fragments,  the  entire  leaf 
must  have  been  40  to  50  cm.  in 
length  before  being  broken.  The 
upper  surface  showed  a  strongly 
marked  furrow  2  to  2\  mm.  in 
width.  The  lower  surface  of  the 
leaf  was  marked  by  a  carene  about 
2  mm.  wide  and  on  either  side  of 
this  there  was  a  well-defined  crease, 
probably  the  stomatiferous  crease 
previously  described  by  Renault. 

Dichotomous  branching  has  been 
found  in  this  genus  but  stems  are 
frequently  single. 

In  the  matter  of  reproductive 
organs  it  has  been  observed  that 
the  regular  bands  of  leaf  scars  are 
frequently  curved  or  irregular  and 
that  lying  between  them  there  are  other  scars  which  are  rounded  or 
angular  and  which  differ  considerably  from  the  leaf  scars.  These 
are  supposed  to  be  the  scars  left  by  the  organs  of  fructification.  Much 
interest  has  been  attached  to  Zeiller's2  discovery  of  Sigillarian  cones 

1  White,  D.,  Flora  of  the  outlying  carboniferous  basins  of  Southwestern  Missouri. 
U.  S.  Geol.  Survey,  Bull.  98,  p.  103,  1893. 

2  Zeiller,  R.,  Cones  de  fructification  des  Sigillaires.     Ann.  des  Sci.  Nat.,  Ser.  6,  Tome 
19,  1884. 


FIG.    44.  —  Calamites  cistii  (Urong- 
(After  Lesquereaux  Pa.   Geol. 


196  FOSSIL   FLORA   OF   THE   COAL-FORMING   PERIODS 

on  long  stalks  with  the  leaves  bearing  sporangia  standing  out  from 
the  stem.  Since  he  could  only  find  macrospores  he  considers  either 
that  these  trees  were  homosporous,  or  that  the  two  types  of  spores 
were  produced  on  different  cones  and  the  macrospore  cones  were  not 
found.  The  discovery  of  these  cones  has  led  some  botanists,  such  as 
Renault,  to  regard  some  of  the  Sigillariae  as  closely  related  to  the 
cycads,  but  such  relation  has  not  been  substantiated. 

Geologic  and  geographic  distribution:  Sigillaria  did  not  make  its 
appearance  in  Europe  before  the  beginning  of  the  Carboniferous,  and 
very  few  specimens  are  found  in  the  Millstone  Grit.  It  seems  to 
have  reached  a  climax  about  the  middle  of  the  Coal  Measures  and 
then  declined.  The  Rothliegende  is  probably  the  latest  formation 
in  which  remains  are  found.  This  family  is  not  mentioned  as  oc- 
curring in  Australia  or  New  Zealand  and  it  seems  to  be  considerably 
more  restricted  geologically  and  geographically  than  Lepidodendron. 
In  North  America  only  two  species  reach  the  Permian  and  they  dis- 
appear early  in  that  period. 

Stigmaria  ficoides  (Brongniart)  :x  The  fossils  known  as  Stigmaria 
were  in  early  days  thought  to  be  a  genus  of  plants.  They  are  ex- 
tremely abundant  in  the  "  sea  tear  th  "  under  the  coal  seams  of  many 
fields,  and  the  finding  in  England  of  these  bodies  actually  attached  to 
stumps  of  Sigillaria  and  Lepidodendron  has  settled  their  derivation. 
They  are  probably  the  roots  of  a  few  other  genera  also  and  it  is  in- 
teresting to  see  how  similar  are  the  roots  of  so  many  of  these  trees. 
The  scars  on  the  roots  are  the  markings  of  the  rhizomes  or  rootlets, 
and  specimens  have  been  found  with  dichotomous  branches  (Fig.  41). 
Very  often  these  roots  when  broken  open  exhibit  a  cylindrical  body 
which  readily  separates  from  the  exterior  coating  and  which  seems 
to  be  a  cast  of  the  central  cylinder. 

(2)  Sphenophyllales.  —  The  Sphenophyllales  are  not  represented 
by  a  living  species.  The  only  genus  is  Sphenophyllum  (Brongniart)2 
which  is  well  represented  by  fossils  in  the  Coal  Measures.  There 
has  been  much  difference  of  opinion  regarding  its  relations.  Some 

1  Renault,  B.,  et  Grand'Eury,  Etude  sur  les  Stigmaria,  rhizomes  et  racines  de  Sigil- 
laries.     Annales  des  Sciences  geologiques,  Tome  12,  1881. 

2  White,  D.,  Op.  cit.,  p.  35;  Coemans,  E.  et  Kick,  J.  J.,  Monographic  des  Sphenophyl- 
lum d'Europe,  Bull,  de  1'Acad.  Roy.  d.  Belgique,  2me  Ser.,  Tome  18,  p.  134,  1864;  also 
Newberry,  J.  S.,  The  Genus  Sphenophyllum.     Jour.  Cincinnati  Soc.  Nat.  Inst.  XIII, 
p.  212,  1891. 


SPHENOPHYLLALE3 


197 


botanists  consider  it  as  most  closely  related  to  the  Lycopodiaceae 
while  others  regard  it  as  being  more  nearly  related  to  Calamariae. 
Members  of  this  genus  are  herbaceous,  the  stems  are  simple  or  branched, 
and  the  surface  is  canaled.  The  leaves  are  in  verticils  on  the  strongly 
marked  articulations  and  in  groups  of  three.  The  leaves  are  sessile 
as  a  rule  but  they  may  occur  on  pedicles.  Those  on  the  stipe  are 
different  from  those  on  the  habetas. 


FIG.  45.  —  i,  ia  Sphenopteris  subalata  (Gein);  2,  2b,  S.  brittsii  sp.  nov.;  3-40,, 
S.  goniopteroides sp.  nov.;  5, 50,  S.  hoeninghausi  (Brongniart);  6,  6a,  S.  elegans (Brong.) ; 
7,  fa,  S.  larischi  (Stur);  8-pa,  S.  tridactylites  (Brong.).  (After  Lesquereaux,  Pa. 

Geol.  Survey.) 

The  center  of  the  stem  consists  of  a  triangular  axis  made  up  of  three 
vascular  bundles.  Exterior  to  these  is  a  ring  of  large  aqueous  tubes 
with  lateral  tangential  growth. 

The  bark  is  thin,  lacuneous  and  generally  poorly  preserved.  The 
branches  are  single  on  articulations.  The  roots  are  cylindrical  and 
the  arrangement  of  the  wood  in  them  is  much  like  that  of  the  stem. 

The  sporangia  are  borne  on  the  bracts  at  some  distance  from  the 


1 98  FOSSIL   FLORA   OF   THE    COAL-FORMING   PERIODS 

axis  and  are  marked  at  the  point  of  attachment  by  a  small  circular 
umbilical  depression.1 

Geologic  and  geographic  distribution:  In  Europe  Sphenophyllum 
extends  from  the  Culm  to  the  lower  Rothliegende  and  was  a  very 
prominent  genus  in  the  middle  and  upper  Coal  Measures.2  It  is  not 
mentioned  as  occurring  in  Australia.  In  North  America  this  genus 
occurs  from  the  lower  Coal  Measures  to  the  Permian. 

(3)  Equisetales.  —  The  Equisetales,  or  horsetails,  include  the 
order  Equisetineae,  which  in  turn  includes  the  family  Calamarieae. 
This  group,  which  formed  a  great  arborescent  flora  in  the  Paleozoic, 
is  now  represented  by  the  single  genus  Equisetum,  a  genus  of  small, 
insignificant  plants  preserving  many  of  the  characteristics  of  the 
fossil  trees  and  commonly  known  as  scouring  rushes. 

Of  the  Calamarieae  Renault  states  that  these  include  all  fossil 
plants,  either  Cryptogams  or  Phanerogams,  which  present  a  cala- 
mi toid  stem,  i.e.,  a  stem  of  which  the  central  part  is  occupied  by  a 
relatively  voluminous  pith,  its  length  being  divided  into  a  series  of 
similar  articulations  which  may  or  may  not  be  related  to  the  articul- 
ations of  the  sheath.3  He  would  then  divide  the  Calamarieae  into 
two  divisions,  the  Equisetinees  and  the  Calamodendrees.  The  first 
would  include  the  articulated  plants  containing  only  primary  wood, 
some  of  which  reproduce  by  simple  spores,  i.e.,  are  isosporous,  like 
the  modern  Equisetum,  while  others  carry  both  microspores  and 
macrospores.  As  examples  the  genera  Annularia  and  Asterophyl- 
lites  are  cited,  (Fig.  42).  Catamites  apparently  belongs  here  also. 
The  second  division  includes  those  which  have  the  secondary 
wood  more  or  less  well  developed  and  which  in  their  organs  of  fructi- 
fication more  nearly  approach  the  phanerogamic  plants  than  do  those 
of  the  other  division.  Of  the  family  Calamarieae,  Calamites  (Suc- 
kow)  (Fig.  43),  and  Annularia  (Sternberg)  are  the  best  known  genera. 
Other  genera  are  Pinnularia,  Asterophyllites,  and  C alamo phyllites. 

In  these  plants  the  surface  of  the  stems,  the  roots  and  their  branches 
are  marked  by  ribs  and  longitudinal  furrows.  The  bark  appears 
smooth  but  little  furrows  may  be  found.  In  some  species  the  furrows 

1  Renault,  B.,  Bassin  houiller  et  Permian  d'Autun  et  d'Epinac.     Flore  Fossile,  Text 
and  Atlas,  Fasc.  IV. 

2  Solms-Laubach.     Op.  cit.,  p.  343. 
8  Renault,  B.,  Op.  cit.,  p.  60. 


EQUISETALES 


199 


PLATE  VIII. 


Pecopteris  (Asterotheca)  abbreviata  (Brongniart.)  i,  Illustrating  the  gradual 
dividing  of  the  pinnules  near  the  inner  end  of  the  frond;  j,  4  Fertile  pinnules;  4  B 
Spores  enlarged  40  times.  Coal  Measures  of  northern  France.  (After  Zeiller.) 


2OO 


FOSSIL  FLORA  OF  THE   COAL-FORMING  PERIODS 


alternate  at  the  joints  and  in  some  they  do  not.  The  roots  have  an 
organization  similar  to  that  of  the  stem  and  frequently  the  aerial 
stems  rise  from  articulations  of  the  roots.  The  racines  and  leaves  are 
arranged  in  verticils  at  each  node  on  the  root,  stem,  or  branch.  The 
leaves  are  simple  and  uninerved,  sometimes  free  and  sometimes  in  a 
collarette  along  the  stem  and  branches.  Sporangiae,  attached  to  the 
borders  of  transformed  leaves,  are  generally  disposed  in  numerous 
verticils  connected  and  forming  the  cone. 


FIG.  46.  —  i  Odontopteris  alata  (Lesquereaux) ;  2  O.  brardii?  (Brongniart) ;  3,  4  O. 
sphenopteroides  sp.  nov.;  5,  6  O.  subcrenulata  sp.  nov.;  7,  ?a  O.  abbreviata  sp.  nov.; 
8  O.  aequalis  (Lesq.)  (After  Lesquereaux,  Pa.  Geol.  Survey.) 

These  plants  are  believed  to  be  isosporous  like  the  modern  represent- 
atives of  this  group. 

Geologic  and  geographic  distribution:  Calamites  and  Annularia 
seem  to  have  made  their  appearance  with  the  Carboniferous  rocks, 
although  members  of  the  Equisetales  were  present  in  the  Devonian 
formation  and  extended  through  that  system  and  into  the  Permian. 
They  were  extremely  important  in  the  Carboniferous  and  representa- 


FILICALES,   OR   FERNS 


201 


tives  of  the  Equisetales  have  continued  to  flourish  through  the  geologi- 
cal periods  to  the  present  day.  They  continued  to  form  large  trees 
until  the  end  of  the  Jurassic  period,  but  in  the  Cretaceous  they  de- 
generated into  small  plants.  As  well  as  having  extensive  geological 
distribution  these  plants  were. widely  distributed  in  Australia,  Asia, 
Europe,  and  America 


FIG.  47.  —  Neuropteris  heterophylla  (Brongniart)  showing  the  development  of  primary 
and  secondary  pinnules.    Coal  Measures  of  France.     (After  Zeiller.) 

(4)  Filicales,  or  Ferns.  —  As  previously  intimated,  the  Filicales 
are  divided  into  two  groups,  the  Filicineae  or  "  true  ferns  "  which 
are  homos  porous,  and  the  Hydropteridineae  or  "  water  ferns,"  which 
are  heterosporous.  The  true  ferns  include  such  types  as  the  royal 
ferns,  tree  ferns,  filmy  ferns  and  ringless  ferns.  The  members  of  the 
group  extend  from  the  Devonian  period  to  the  present  and  some 
of  them  were  very  prominent  in  the  coal  measures  of  various  periods. 


2O2 


FOSSIL  FLORA  OF  THE   COAL-FORMING  PERIODS 


They  may  be  arborescent  or  herbaceous,  the  height  of  some  of  the 
arborescent  varieties  being  as  much  as  20  meters. 

The  classification  of  the  living  ferns  is  based  chiefly  on  the  nature 
of  the  sporangia.  Zeiller1  states  that  on  this  basis  ferns  may  be 
divided  into  two  large  groups,  Leptosporangiae  or  the  ferns  proper, 
and  Eusporangiae  or  Marattiadiae.  In  the  former  group  each  spo- 
rangium springs  from  only  one  epidermic  cell  and  when  it  is  ripe  the 


FIG.  48. —  i,  4,  5,  7,  9,  12  Neuropteris  hirsuta  (Lesquereaux) ;    2,  5,  6,  8,  10,  n,  N. 
angustifolia  (Brongniart).     (After  Lesquereaux  Pa.  Geol.  Survey.) 

walls  are  formed  of  only  one  layer  of  cells.  In  the  latter  sub-class 
each  sporangium  proceeds  from  a  subepidermal  cell,  and  when  mature 
the  walls  are  relatively  thick  since  they  are  constituted  of  several 
layers  of  cells. 

In  the  case  of  fossil  ferns  it  is  generally  necessary  to  follow  Brong- 
niart's  system2  and  classify  them  according  to  the  nature  of  the  fronds 

1  Zeiller,  R.,  Bassin  houiller  et  Permien  d'Autun  et  d'Epinac.    fitudes  des  gites 
mine'raux  de  la  France.     Fasc.  II,  Pt.  I,  Flore  Fossile,  (FougSres)  1890. 
*  Brongniart,  A.,  Histoire  des  vegetaux  fossiles,  1828. 


FELICALES,   OR   FERNS  203 

and  the  nervation  since  the  organs  of  fructification  are  infrequently 
preserved.  One  of  the  striking  features  of  all  ferns  is  the  highly 
divided  character  of  the  leaves.  The  method  of  division  has  been 
used  as  a  means  of  classification  by  Brongniart  and  others,  but  that 
system  is  not  very  satisfactory.  The  organs  of  fructification,  or 
sporangia,  where  preserved,  are  found  on  the  under  side  of  leaves  and 
form  little  globular  sacs  containing  a  considerable  number  of  spores 
which  are  set  free  by  rupture  of  the  wall  of  the  sporangium.  The 
spores  give  rise  to  the  prothallium,  a  vegetative  apparatus  which 
carries  both  the  male  and  female  organs. 

On  the  basis  of  the  manner  of  attachment  of  the  pinnules  and  the 
nervation  the  ferns  may  be  divided  into  the  following  six  groups:1 

1.  Sphenopteridae,  in  which  the  frond  is  finely  divided  and  the 

pinnules  are  small; 

2.  Pecopteridae  with  pinnules  attached  to  the  rachis  for  all  their 

width; 

3.  Odontopteridae  with  pinnules  equally  fixed  to  the  rachis  for 

all  their  width  but  without  the  distinct  median  nerve; 

4.  Neuropteridae  with  pinnules  generally  quite  large,   rounded, 

and  often  notched  in  the  center  of  their  base,  attached  at 
only  one  point; 

5.  Teniopteridae  with  simple  fronds,  ribboned,  much  longer  than 

wide,  the  edges  entire  or  feebly  crenulated; 

6.  Dictyopteridae,   including   all   forms   in   which   the   nervation 

anastomoses  and  forms  a  more  or  less  complex  network  in- 
stead of  remaining  separate. 

In  cases  where  the  organs  of  fructification  have  been  found,  a  more 
logical  and  genetic  arrangement  may  be  made,  but  the  classification 
has  never  been  satisfactory. 

Following  unsatisfactory  attempts  to  classify  the  ferns  thus,  re- 
cent work  by  Grand'Eury,  White,  Kidston,  Oliver  and  Scott  has 
shown  that  many  of  these  plants  are  not  ferns  and  that  they  should 
be  placed  with  the  Gymnosperms  as  the  most  primitive  of  these 
plants.  For  those  plants  which  bear  seeds  and  which  had  formerly 
been  called  Cycadofilices  because  they  combined  in  the  stem  the 

1  Zeiller,  R.,  Op.  cit. 


204 


FOSSIL   FLORA  OF  THE   COAL-FORMING   PERIODS 


characters  of  ferns  and  cycads,  Oliver  and  Scott1  have  proposed  the 
name  Pteridospermae.  In  this  group  Zeiller2  considers  that  there 
should  be  placed  several  of  the  Sphenopteridae,  some  Pecopteridae 
such  as  Pecopteris  fluckeneti  and  Pecopteris  sterzeli,  probably  all  the 
Alethopteridae  comprising  probably  Callipteridium  and  Callipteris, 
also  all  the  Odontopteridae  and  Neuropteridae.  He  considers  that 
it  would  be  easy  to  change  the  two  last-named  families  but  there  is 
much  uncertainty  about  many  of  the  others  such  as  the  Alethopteridae, 


FIG.  49.  —  Taeniopteris   Newberriana    sp.  nov.     From  the  Permian.     (After  Fontaine 

and  White,  Pa.  Geol.  Survey.) 

and  that  three  groups  might  be  made,  including  the  Filicineae,  the 
uncertain  forms  and  the  Pteridosperms.  In  this  division  Zeiller 
would  leave  with  the  ferns  those  plants  whose  fronds  carried  the  fili- 
coid  fructifications  but  whose  male  apparatus  is  like  that  of  the  Pteri- 
dosperms. 

Geologic  and  geographic  distribution:     The  ferns  made   their  ap- 
pearance in  the  early  Devonian  and  reached  a  fairly  high  state  of 

1  Oliver,  F.  W.,  and  Scott,  D.  H.,  On  Lagenostoma  Lomaxi,  the  seed  of  Lyginodendron. 
Proc.  Roy.  Soc.  London  LXXI,  p.  477,  1903.  LXXIII,  p.  4,  1904;  also  On  the  structure 
of  the  Paleozoic  seed  Lagenostoma  Lomaxi.     Phil.  Trans.  Roy.  Soc.  London,  Ser.  B., 
Vol.  197,  p.  193,  Pis.  4  to  10,  1904. 

2  Zeiller,  R.,  Bassin  houiller  et  Permien  de  Blanzy  et  du  Creusot,  Etudes  des  gftes 
MinSreaux  de  la  France,  Fasc.  II,  Flore  Fossile,  Text  et  Atlas. 


FILICALES,   OR   FERNS 


205 


development  in  that  period.     They  increased  in  numbers  01  species 
and  in  individuals  in  the  Carboniferous  and  while  none  of  the  typical 


FIG.  50.  —  i   Alethopteris   serli   (Brongniart) ;    j,  A.   decurrens    (Artes).     These  forms 
illustrate  the  different  forms  of  the  pinnules  in  this  genus.     (After  Zeiller.) 

Carboniferous  species  extended  beyond  the  Permian  other  species 
of  the  same  genera  have  occupied  a  prominent  position  in  the  world's 
flora  during  the  Triassic  and  Jurassic  periods  and  still  others  have 


206 


FOSSIL   FLORA   OF   THE   COAL-FORMING   PERIODS 


carried  the  succession  to  the  present  time.     They  have  been  found 
in  probably  every  country  in  which  plant  remains  are  abundant 

(4)     THE    SPERMATOPHYTES 

The  Spermatophytes  include  the  two  great  groups  of  highly  organ- 
ized seed  plants,  the  Gymnosperms  and  the  Angiosperms.  They  are 
often  called  Phanerogams  or  "  flowering  plants." 

GYMNOSPERMS 

The  Gymnosperms  include  a  great  variety  of  plants,  from  shrubs 
to  large  trees,  and  they  have  had  representatives  from  middle  Paleo- 
zoic time  to  the  present.  They  are  characterized  by  their  naked  seeds 


FIG.  51.  —  Lonchopteris  bricei  (Brongniart)  showing  the  terminal  pinnules  and  the 
changes  occurring  in  the  pinnules  with  maturity.  From  the  Coal  Measures  of  France. 
(After  Zeiller.) 

in  contrast  to  the  Angiosperms  which  have  the  seeds  enclosed.  The 
main  groups  of.  Gymnosperms  are  (i)  Cycadofilicales ,  (2)  Bennettitales , 
(3)  Cycadales,  (4)  Cordaitales,  (5)  Gingkoales,  (6)  Coniferales,  and 
(7)  Gnetales.  Of  these  groups  the  Cycadofilicales,  the  Bennettitales, 
and  the  Cordaitales  are  all  extinct. 

(i)  Cycadofilicales:    As  already  mentioned  in  the  discussion  on 


GYMNOSPERMS  207 

ferns,  there  have  been  found  during  this  century  numerous  plants 
which  were  formerly  thought  from  their  frond  character  to  be  ferns 
but  which  have  been  grouped  together  to  form  the  Pteridosperms 
because  of  the  discovery  of  their  seeds.  They  are  believed  to  be  the 
most  primitive  of  the  seed  plants,  and  from  them  the  modern  Gym- 
nosperms  developed.  They  show  a  transition  between  the  ferns 
and  cycads  and  they  differ  from  the  ferns  in  having  secondary  wood. 
This  secondary  wood  is  still  a  Pteridophyte  character  in  some  groups 
although  it  is  also  a  characteristic  of  the  Gymnosperms.  The  micro- 
sporangia  are  similar  to  those  of  the  ferns  but  the  macros porangia  are 
very  different  since  an  ovule  is  developed.  As  the  members  of  this 
group  have  been  differentiated  so  recently  and  as  there  is  so  much 
uncertainty  about  which  genera  and  species  should  be  placed  with 
the  Pteridosperms  and  which  with  the  ferns,  it  is  impossible  to  state 
definitely  their  geological  range.  They  appeared  at  least  as  early  as 
the  Upper  Devonian,  became  extremely  abundant  in  the  Carbonifer- 
ous, extended  into  the  Permian  and  probably  into  the  Mesozoic. 

(2)  Bennettitales  and  (3)  Cycadales:  Bennettitales  is  the  name 
applied  by  some  botanists  to  a  group  of  extinct  Mesozoic  plants  which 
are  regarded  as  the  ancestors  of  the  living  cycads.  In  his  monograph 
on  the  fossil  cycads,  Wieland1  stated  that  in  the  opinion  of  Scott  and 
Zeiller  the  Bennettitales  should  not  be  regarded  as  a  separate  class 
and  that  his  work  has  verified  the  opinion  of  these  botanists  and  his 
own  earlier  expressed  opinion.  He  had  formerly  believed  that  Cycad- 
ales should  include  the  existing  families  Cycadeae  and  Zamiae  form- 
ing the  order  Cycadaceae,  and  the  extinct  family  Bennettiteae  which 
might  have  the  rank  of  an  order. 

The  living  forms  of  cycads  are  tropical  plants  and  they  occur  in 
both  the  Eastern  and  Western  Hemispheres.  Common  genera  are 
Cycas  and  Zamia. 

The  family  Cycadeoideae  or  the  Bennettiteae  have  been  reported 
from  the  Triassic,  the  Jurassic,  and  lower  Cretaceous  of  America 
and  they  have  a  similar  range  in  Europe  and  Asia. 

The  representatives,  such  as  Zamites,  of  the  living  families  of 
cycads  have  been  found  as  far  back  as  the  Coal  Measures.2  They 

1  Wieland,  G.  R.,  American  fossil  cycads,  Carnegie  Inst.  of  Washington,  p.  236,  1906. 

2  Renault,  B.,  et  Zeiller,  R.     Sur  quelques  cycadees  houilleres.     Comptes  rendus  de 
Pacad.  de  Paris,  1886. 


208 


FOSSIL   FLORA   OF   THE    COAL-FORMING   PERIODS 


increased  in  numbers  through  the  Permian  and  reached  a  maximum 
development  in  the  Jurassic  which  is  often  spoken  of  as  the  "  Age  of 
Cycads."  They  have  had  a  very  wide  geographical  distribution. 
(4)  Cordaitales:  The  Cordaitales  formed  the  main  portion  of  the 
arborescent  Gymnosperm  vegetation  of  the  later  Paleozoic.  They 
comprised  rather  slender  trees  which  were  of  uniform  size  for  10  or 
15  meters,  but  reached  upwards  of  30  meters  in  height  and  were 
crowned  by  numerous  branches.  The  genus  Cordaites  (Unger)  may 


FIG.  52.  —  Cycadeoidea  marshiana   showing  stages   in   fruit  production  as  shown  in 
branching  species.     (After  Wieland,  American  Fossil  Cycads.) 

be  taken  as  the  typical  representative  of  the  group.  The  leaves  are 
simple  and  are  characterized  by  distinct  parallel  nervation,  often 
becoming  complex.  They  resemble  those  of  the  Cycads  in  exhibiting 
the  characteristic  mesophyll,  and  those  of  the  Coniferae  in  the  form 
of  the  leaf,  which  is  long,  usually  rounded  at  the  outer  end  and  narrow- 
ing towards  the  base. 

The  stem  and  branches  are  provided  with  a  large  medullar  sheath 
cut  by  transverse  diaphragms  of  the  pith.  There  is  a  thick  cylinder 
of  secondary  wood. 

In  the  structure  of  the  ovule  and  the  swimming  sperms  they  re- 
semble the  Cycads  and  Gingkos  which  are  the  only  living  plants 


GYMNOSPERMS 


209 


with  these  sperms.  Their  structure  has  been  studied  in  detail  by 
Grand'Eury,  and  Renault,  and  to  them  chiefly  we  owe  our  knowledge 
of  the  reproductive  organs. 

Geologic  and  geographic  distribution:    The  Cordaiteae  appeared  in 
the  Devonian  in  America,1  Europe  and  Australia.     It  seems  possible 


FIG.  53.  —  Cordaites  showing  the  leaves  and  organs  of  fructification.    (After  Grand' 
Eury.    Flore  Carbonifere  du  Departement  de  la  Loire.) 


that  they  may  have  lived  as  early  as  the  Middle  Devonian.     They 
were  abundant  in  the  upper  Coal  Measures  and  continued  into  the 

1  Dawson,  J.  W.,  On  Fossil  Plants  from  the  Devonian  Rocks  of  Canada.     Quart. 
Jour.  Geol.  Soc.  of  London,  Vol.  15,  1859. 


210 


FOSSIL  FLORA  OF  THE   COAL-FORMING  PERIODS 


Permian,  but  it  is  not  believed  that  they  survived  the  close  of  the 
Paleozoic. 

(5)  Gingkoales:  This  order  of  Gymnosperms  is  represented  by  a 
single  living  species,  Gingko  biloba,  found  wild  in  China  and  culti- 
vated by  the  Chinese  and  Japanese.  The  fossil  forms  of  this  group 


FIG.  54.  —  Walchia  frondosa  (B.  Renault)  showing  small  cones.  From  the  Permian  of 
France.  (After  B.  Renault,  Bassin  Houiller  et  Permien,  Etudes  des  Gltes  Min6raux 
de  la  France.) 


have  frequently  gone  under  the  name  of  the  Salisburias.  They  have 
probably  been  derived  from  the  Cordaitae  and  they  were  abundant 
in  the  Mesozoic,  being  mentioned  as  occurring  in  the  Oolite  and  the 
Chalk  of  Europe,  and  in  the  Triassic  and  Jurassic  of  Australia.1 

1  Siissmilch,  C.  A.,  An  introduction  to  the  geology  of  New  South  Wales,  pp.  164  and 
175,  1914. 


GYMNOSPERMS 


211 


(6)  Coniferales:  This  group  of  plants  is  so  well  known  at  the 
present  day  that  they  scarcely  need  a  detailed  description.  They 
are  characterized  primarily  by  their  cones  although  other  plants, 
such  as  some  of  the  Pteridophytes,  may  have  cones  of  a  certain  kind. 
Most  of  these  trees  are  evergreens,  as  the  pines,  hemlocks,  spruces, 
and  cedars  but  some,  like  the  tamarack,  are  deciduous.  Most  of 
them  have  needle  leaves  which  are  specially  adapted  to  the  rigors  of 
northern  climates.  The  stem  is  a  single,  central  stalk  extending  to 
the  top  of  the  tree. 

There  are  two  families  (i)  Taxaceae  and  (2)  Pinaceae.  The  mem- 
bers of  the  former  family  usually  have  fleshy  seeds  and  ovules  freely 


FIG.  55.  —  Leaves  of  plants  from  the  Glossopteris  flora. 
(6)  Glossopteris.     (c)  Rhacopteris. 


(a)  Gangamopteris. 


exposed  and  those  of  the  latter  family  have  dry  seeds  and  ovules 
concealed  by  scales. 

The  Pinaceae  may  again  be  divided  into  four  groups  well  repre- 
sented by  living  forms:  (i)  Abietineae,  including  pines,  spruces, 
hemlocks,  firs,  cedars,  and  larches;  (2)  Taxodineae,  including  Sequoia 
and  Taxodium  (bald  cypress  common  in  our  southern  swamps); 
(3)  Cupressineae,  including  the  arbor  vitae,  and  the  juniper;  (4) 
Araucarineae,  including  the  Araucarian  pines  so  frequently  seen  in 
New  Zealand. 

Representatives  of  the  Coniferae  extend  back  into  Devonian  beds, 
but  it  is  not  always  easy  to  place  the  fossil  forms  in  the  groups  men- 
tioned above  and,  furthermore,  the  wood  of  the  Coniferae  may  in 


FIG.  56.  —  Leaves  illustrating  the  development  of  the  modern  types  of  plants  in  the 
later  geological  periods,  a,  Macro taenopteris  magnifolia  (Rogers),  Triassic  coal 
beds  of  Virginia  (Fontaine);  b,  Gingko  digitata  (Herr),  Jurassic;  c,  Cinnamomum 
Lesperium  (Knowlton);  d,  Aralia  veatchii  and  e,  Rhamnus?  Williardi  (Knowlton),  Upper 
Cretaceous;  /,  Fagara,  catahoulensis  major  (Berry)  and  g,  Ulmus  floridana  (Berry), 
Oligocene;  h,  Quercus  chapmanifolis  (Berry),  Miocene  (U.  S.  Geol.  Survey.)  212 


THE   ANGIOSPERMS  213 

some  cases  be  confused  with  that  of  the  Cordaites  as  there  is  a  close 
relationship  between  the  groups,  Cordaites  and  Coniferae.  The 
Taxaceae  do  not  seem  to  have  extended  backward  beyond  the  Jurassic. 
The  Cupressineae  have  been  found  as  far  back  as  the  Jurassic.  The 
well-known  extinct  genus  Voltzia  probably  belonged  to  the  Araucar- 
ineae  and  extended  back  into  the  Permian.  Walchia  is  a  conifer  from 
the  Permian.  The  Sequoias  have  been  found  from  the  early  Cret- 
aceous onward  and  were  abundant  in  the  early  Tertiary.  Taxodium 
probably  extended  from  the  Oligocene  to  the  present.  The  Coniferae 
have  been  widely  distributed  over  the  globe. 

THE  ANGIOSPERMS 

This  great  group  of  plants,  representing  the  climax  in  plant  evol- 
ution, was  ushered  in  with  the  Cretaceous  period.  They  have  de- 
veloped so  rapidly  and  they  now  occupy  such  an  important  and  com- 
mon place  in  the  living  vegetation  that  any  attempt  to  describe  them 
here  would  be  futile.  Their  representatives  are  found  in  every 
formation  where  plant  fossils  occur  since  the  beginning  of  the  Lower 
Cretaceous  period,  and  they  now  outnumber  the  Gymnosperms  several 
hundred  times.  The  common  trees,  outside  of  the  Conifers,  belong 
to  this  group,  as  do  the  grasses  and  the  other  common  flowering  plants 
with  which  everyone  is  so  familiar. 


CHAPTER  VIII 
STRUCTURAL  FEATURES   OF   COAL   SEAMS 

Thickness  of  Seams 

Coal  beds  vary  from  a  fraction  of  an  inch  to  the  enormous  thickness 
of  266  feet.  At  Morwell,  Victoria,  Australia,  there  are  three  seams 
of  brown  coal  which  are  266,  227,  and  166  feet  respectively,  in  thick- 
ness. They  are  the  thickest  so  far  known  in  the  world.  A  drill 
hole  1010  feet  deep  passed  through  780  feet  of  coal.  Other  notable 
beds  are  the  Grande  Couche  of  Commentry,  central  France,  which  is 
60  feet  thick,  and  the  Mammoth  seam  of  the  anthracite  region  of 
Pennsylvania,  which  in  the  Southern  Field  reaches  50  feet  in  thick- 
ness. Seams  in  Styria  and  Manchuria  exceed  100  feet  in  places. 
Most  seams  vary  rather  rapidly  in  thickness  from  place  to  place,  the 
Pittsburgh  bed  of  the  Appalachian  province  being  probably  the  most 
remarkable  exception  to  this  rule.  This  seam  has  been  traced  over 
an  area  of  more  than  2100  square  miles  with  an  average  thickness  of 
over  7  feet.  Its  total  original  area  has  been  estimated  at  about 
30,000  square  miles.  The  irregularities  in  the  thickness  of  seams  are 
due  chiefly  to  the  structures  known  as  "  partings,"  "  pinches  "  or 
"squeezes/'  "  swells,"  "  horsebacks,"  "rolls,"  "clay  veins"  and 
"  cut-outs  "  and  to  igneous  intrusions. 

Partings.  —  A  seam  may  be  divided  into  several  thinner  seams  or 
"  splits  "  by  partings  of  clay,  shale,  slate,  or  sandstone,  (Fig.  57). 
For  example,  the  Mammoth  seam,  which  reaches  a  thickness  of  50 
feet  in  the  eastern  part  of  the  Southern  Field  is  divided  into  three 
splits  at  the  western  end,  averaging  about  10,  12  and  15  feet  respec- 
tively, in  thickness,  with  partings  of  slate  between  them  running  from 
10  to  30  feet  in  thickness.  These  splits  would  be  regarded  as  indi- 
vidual seams  were  it  not  for  the  fact  that  they  can  be  traced  into  the 
main  seam  to  the  eastward.  Other  seams  are  known  in  which  the 
number  of  splits  is  very  much  larger  than  in  the  case  cited. 

The  splits  are  due  to  the  fact  that  while  the  vegetal  matter  is  being 
laid  down  in  the  swamp  or  open  body  of  water  there  are  periods 

214 


PINCHES  215 

when  clay  or  sand  is  brought  in  by  water  from  the  surrounding  lands 
and  carried  out  over  the  vegetal  matter.  The  deposit  of  sediment 
grows  thinner  as  it  extends  away  from  the  dry  land  and  some  distance 
from  the  edge  of  the  basin  the  deposition  of  vegetal  matter  goes  on 
without  interruption  so  that  a  continuous  coal  seam  results,  whereas 
closer  to  the  edge  the  seam  is  interrupted  by  these  bands  of  sediment. 
The  number  of  partings  will  depend  upon  the  rate  of  change  in  level 
between  the  surrounding  land  and  the  basin,  or  upon  the  variations 
in  climate.  A  sinking  of  the  basin  where  the  vegetal  matter  is  being 
deposited  or  a  rise  of  the  surrounding  land  will  cause  sediment  to  be 


FIG.  57.  —  Diagram   illustrating:     C,    cut-out;    H,    horsebacks;     P,   parting;    R,   roll; 

S,  split;   V,  clay  vein. 


carried  out  by  streams  farther  from  the  edge  of  the  swamp  or  other 
basin  than  it  was  formerly,  while  a  change  to  a  wetter  climate  may 
also  cause  greater  erosion  of  the  land  and  consequently  a  more  ex- 
tended deposition  of  sediment  over  the  vegetal  matter  in  the  swamp. 
"  Pinches  "  or  "  squeezes,"  and  "  swells." — These  are  terms 
applied  to  sections  in  the  seam  where  it  has  become  constricted  by 
the  squeezing  in,  or  extended  by  the  bulging  out  of  the  overlying  or 
underlying  rocks.  They  are  due  to  pressure  applied  to  the  seam  during 
the  folding  and  other  movements  of  the  enclosing  strata  and  they 
may  accompany  the  formation  of  "  horsebacks  "  and  similar  struc- 
tures. 


2l6 


STRUCTURAL  FEATURES  OF  COAL  SEAMS 


"  Cut-outs."  —  This  is  a  term  applied  by  miners  to  any  place  in 
the  seam  where  the  coal  ends  abruptly  on  account  of  faulting,  squeez- 
ing, or  erosion.  It  may  be  used  in  a  more  restricted  sense  for  the 
case  where  part  of  the  bed  has  been  removed  by  erosion,  (Fig.  57). 
It  often  happens  that  a  coal-bearing  formation  suffers  erosion  and  a 
stream  cuts  a  ravine  through  one  or  more  beds  of  coal.  This  ravine 
may  be  filled  later  by  sand  or  clay  carried  in  by  the  stream,  or  a 
glacier  passing  over  it  may  fill  it  with  drift  consisting  of  a  mixture 
of  clay,  sand  and  boulders.  A  fine  example  of  the  latter  phenomenon 
is  found  in  the  Anthracite  Field  of  Pennsylvania.  Before  the  glacier 
appeared  in  this  district  the  Susquehanna  River  flowed  in  a  channel 


FIG.  58.  —  Gorge  of  Des  Moines  River  at  city  of  Des  Moines  illustrating  how  a  cut- 
out may  develop.     (From  Iowa  Geol.  Survey.) 

between  Nanticoke  and  Pittston.  During  Pleistocene  time  the 
glacier  moved  southward  across  this  channel,  which  became  filled 
with  glacial  drift.  The  river  was  thus  forced  to  carve  out  a  new 
channel  for  itself  after  the  glacier  melted  away.  It  has  also  been 
suggested  that  this  abandoned  channel  might  have  been  gouged 
out  by  the  glacier  as  fiords  are  deepened.  The  old  channel  has 
been  well  outlined  as  it  has  caused  much  trouble  in  mining,  owing 
particularly  to  the  large  amount  of  water  contained  in  the  sand  and 
gravel  and  the  bad  condition  of  the  rocks  along  its  edges. 

"  Horsebacks,"  '  'rolls,"  and  "clay  veins."— All  of  these 
names  have  been  used  more  or  less  loosely  for  the  same  structures 
in  coal  mines  in  different  localities.  The  term  "  horseback  "  among 
the  coal  miners  is  used  to  indicate  some  foreign  body  in  the  coal 
seam  in  much  the  same  general  way  as  "  horse  "  is  used  among  the 
metal  miners  to  indicate  a  mass  of  rock  in  the  lode.  It  probably 


HORSEBACKS  217 

arose  from  the  general  rounded  form,  which  is  more  or  less  charac- 
teristic of  these  structures  and  which  suggests  the  arched  back  of  a 
horse.  The  German  miners  use  the  word  "  horst  "  in  much  the  same 
way  as  "  horse  "  is  used  among  the  miners  in  this  country. 

The  names  "  rolls  "  and  "  swells  "  are  very  appropriate  terms  for 
these  structures  because  in  some  mines  these  masses  of  rock  resemble 
nothing  more  closely  than  the  waves  on  the  sea  when  running  as  a 
ground-swell.  The  reason  for  confusing  the  "  clay  vein  "  with  the 
horseback  is  doubtless  due  to  the  fact  that  the  former  in  many  places 
is  an  offshoot  from  a  rounded  mass  of  clay  similar  to  a  typical  horse- 
back, (Fig.  57). 

Several  theories  have  been  offered  to  explain  the  origin  of  horse- 
backs and  it  is  possible  they  have  been  formed  in  at  least  two  ways. 
One  theory,  advanced  by  mining  men  in  some  coal  fields,  is  that 
they  were  formed  by  streams  flowing  into  the  swamps  where  the 
vegetation  giving  rise  to  the  coal  was  being  laid  down.1  These 
streams  would  bring  in  clay  or  sand  and  build  up  long  narrow  ridges 
of  sediment  which  would  become  buried  under  vegetal  matter  as 
the  formation  of  the  coal  bed  progressed.  The  rolls  in  the  roof  are 
explained  as  due  to  a  stream  cutting  a  channel  down  into  the  coal 
seam,  this  channel  later  becoming  filled  with  sediment.  While  this 
explanation  may  account  for  a  few  of  these  structures  it  will  not 
account  for  the  great  majority  of  horsebacks,  as  they  are  undoubt- 
edly due  to  compression  of  the  seam  and  enclosing  rocks,  which  pro- 
duces small  folds  in  either  the  roof  or  floor  of  the  seam  or  in  both. 
When  pressure  is  applied  to  the  floor  it  buckles  up  into  the  coal,  which 
is  less  resistant  than  the  bottom  rock  and,  in  the  early  stages  of  its 
development,  much  more  plastic  than  the  underlying  rocks.  Like- 
wise when  pressure  causes  the  draw  slate  to  buckle  in  the  roof  of  the 
seam  it  bends  down  into  the  coal  (Fig.  57).  A  very  fine  illustration 
of  the  occurrence  of  these  structures  is  seen  in  the  Pittsburgh  seam 
in  the  vicinity  of  Connellsville,  Pennsylvania.2  They  rise  from  6 
inches  to  as  many  feet  above  the  general  level  of  the  floor  of  the  seam 
and  resemble  waves  spread  over  the  floor  of  the  mine  (Plate  IX). 
The  seam  is  everywhere  constricted  above  them  except  in  one  or  two 

1  J.  F.  Blandy,  On  evidence  of  streams  during  the  deposition  of  the  coal,  (horse- 
backs).    Trans.  Amer.  Inst.  Min.  Eng.,  Vol.  4,  p.  113,  1875. 

2  Moore,  E.  S.,  "Horsebacks"  in  Oliver  No.  3  Mine.     Coal  Age,  Vol.  3,  p.  566,  1913. 


HORSEBACKS  219 

places  noted,  where  the  roof  slate  is  bowed  up  above  the  elevation 
in  the  floor.  The  rolls  often  show  lamination  in  the  sediments  where 
the  beds  have  been  bent  and  in  many  of  these  there  are  bunches  of 
pyrite  crystals  which  have  collected  there  because  the  structure  direc- 
ted the  circulating,  iron-bearing  waters  into  these  little  anticlines. 

The  horsebacks  are  not  uniformly  distributed  over  the  floor  of  the 
mine  because  the  rocks  are  not  uniformly  resistant  and  therefore  they 
buckle  in  some  areas  and  resist  buckling  in  others.  Where  there  is 
one  roll  there  are  usually  two  or  more  adjoining  it,  as  in  the  case  of 
waves  on  water,  due  to  the  fact  that  a  large  anticline  should  normally 
have  small  ones  on  either  side  where  it  dies  out.  These  smaller  folds 
result  from  irregularities  in  the  strength  of  the  bed  and  from  the  differ- 
ent angles  at  which  the  force  is  applied  as  the  larger  fold  develops. 
That  these  structures  are  not  deposits  made  by  streams  is  proven 
by  the  fact  that  they  often  occur  entirely  away  from  the  border  of 
the  swamp  in  which  the  coal  vegetation  was  laid  down. 

The  coal  basins  as  they  now  exist  are  not  identical  in  size  or  shape 
with  the  original  basins  but  have  resulted  from  the  folding  of  the  coal 
measures  into  anticlines,  where  there  were  originally  small  elevations, 
and  synclines,  where  there  were  originally  small  depressions  in  the 
strata.  With  subsequent  erosion  of  the  anticlines  the  synclinal  basins 
have  been  separated  from  each  other.  Thus  it  will  be  seen  that  one 
of  these  basins  may  be  near  the  center  of  the  great  swamp  in  which 
the  vegetal  matter  was  originally  laid  down  and  the  horseback  may 
show  no  connection  with  the  land  at  the  border  of  the  original  basin. 

It  is  evident  that  a  direct  relation  may  be  found  between  the  orient- 
ation of  the  horsebacks  and  the  direction  of  the  main  structures  of 
the  basin.  Following  the  general  principles  of  structural  geology  it 
is  known  that  if  a  small  fold  occurs  on  the  flank,  in  the  trough,  or  on 
the  crest  of  a  larger  fold  the  axis  of  the  minor  fold  will  be  in  the  same 
direction  as  the  strike  of  the  rocks  at  that  particular  point  in  the  larger 
fold.  It  was  found  to  be  true  at  Oliver  No.  3  mine,  mentioned  above, 
that  the  axes  of  the  horsebacks  follow  the  strike  of  the  rocks  forming 
the  larger  basin  at  the  point  where  they  occur,  and  inquiries  in  various 
other  mining  regions  where  horsebacks  are  common  elicited  answers 
which  go  to  strengthen  this  assumption  for  the  arrangement  of  these 
structures  in  all  fields.  According  to  this  principle  the  long  axes  of 
the  horsebacks  in  a  pitching  synclinal  basin  would  form,  if  plotted  on 


220         STRUCTURAL  FEATURES  OF  COAL  SEAMS 

a  map  of  the  basin,  an  elliptical  zone  around  the  deepest  point  in  the 
basin.  As  the  center  of  the  basin  is  approached  the  arrangement  of 
the  structures  will  become  much  less  regular  owing  to  the  confusion 
of  forces  which  are  acting  from  various  directions  on  the  rocks  in  the 
center  of  the  basin.  The  establishing  of  this  relationship  between  the 
direction  of  the  horsebacks  and  the  larger  folds  in  the  coal  basins  has 
a  practical  bearing.  It  should  become  possible,  as  our  knowledge  of 
these  structures  increases,  to  predict  the  general  direction  in  which 
the  long  axes  of  the  horsebacks  will  lie  and,  when  the  arrangement  of 
these  is  known,  the  entries  and  butts  in  the  mine  may  be  planned  in 
such  a  way  as  to  avoid  as  much  as  possible  the  cutting  of  these  ridges. 
If  one  must  be  cut  it  may  be  cut  along  its  shorter  axis. 

A  "  clay  vein  "  is  a  body  of  clay  which  fills  a  crevice  in  a  coal  seam, 
(Fig.  57).  It  is  usually  roughly  tabular  like  an  ore  vein,  but  in 
many  cases  it  branches  in  an  extremely  complex  manner,  sending 
stringers  out  in  all  directions  through  the  coal.  It  originates  where 
the  pressure  on  the  floor  or  roof  of  the  seam,  or  on  both,  is  sufficiently 
great  to  force  plastic  clay  into  small  fissures  and  in  many  cases  en- 
large them.  The  clay  often  rises  as  a  mound  on  the  floor  of  the  seam 
so  that  it  resembles  a  horseback  and  if  there  be  a  crack  in  the  overlying 
coal  it  rises  from  the  mound  as  a  vein.  In  some  localities  the  miners 
use  the  word  "  spar  "  for  a  small  clay  vein. 

"Bell,"  "pot,"  "kettle."  — The  terms  "bell,"  "pot,"  and  "kettle" 
are  often  used  for  a  roughly  cone-shaped  or  rounded  mass  of  slicken- 
sided  rock  which  falls  from  the  roof  of  a  seam,  sometimes  causing 
serious  accidents  to  the  miners.  These  bodies  are  also  known  as 
"  camel-backs  "  and  "  tortoises."  They  are,  in  most  cases,  con- 
cretionary structures  containing  pyrite,  iron  oxide,  iron  carbonate  or 
calcite  mixed  with  clay  or  slate  and  they  separate  rather  freely  from 
the  roof  slate.  This  ready  separation  is  apparently  often  due  to 
previous  movement  in  the  strata  as  the  bodies  frequently  show 
slickensided  surfaces  indicating  that  there  has  been  slipping  of  the 
surrounding  rocks  over  the  concretionary  masses.  In  addition  to 
the  concretionary  bodies  which  form  these  structures  in  the  roof  there 
are  certain  harder  or  denser  patches  of  clay  or  sandstone,  which 
separate  from  the  adjacent  rocks  and  fall  from  the  roof,  (Fig.  59). 
Rounded  masses  of  igneous  rock  and  casts  of  trees  occur  in  the  upper 
part  of  the  coal  bed  in  some  regions  and  they  fall  freely  from  the  roof. 


FOLDING  IN   COAL   BEDS 


221 


These  structures  may  all  go  under  the  names  mentioned  above  if 
their  shape,  in  the  opinion  of  the  miner,  happens  to  correspond  to 
that  of  any  of  the  above-named  bodies. 


FIG.  59.  —  Small  coal  stringer,  Paradise  Mine  Duquoin,  111.     (From  Bull,  of  the  111. 
Geol.  Survey,  University  of  111.  and  U.  S.  Bur.  of  Mines.) 

Folding  in  Coal  Beds 

In  any  study  or  discussion  of  folds  two  terms,  dip  and  strike,  are 
much  used.  The  dip  is  the  angle  which  the  bed  makes  with  a  hori- 
zontal plane,  or  in  other  words  the  inclination  of  the  bed  to  a  hori- 


FIG.  60. 


zontal  plane.  The  strike  is,  in  general  terms,  the  direction  of  the 
outcrop,  but  in  many  cases  a  more  accurate  and  concrete  definition 
is  necessary  for  practical  purposes  since  the  strike  must  sometimes 


222 


STRUCTURAL    FEATURES   OF   COAL   SEAMS 


be  determined  in  the  bottom  of  a  mine  shaft  or  elsewhere  where  only 
a  very  small  area  of  the  stratum  is  exposed.  In  such  cases  the  strike 
is  represented  by  a  horizontal  line  on  the  face  of  the  bed  or  in  other 
words  the  strike  is  the  line  along  which  the  bed  intersects  a  horizontal 
plane.  This  line  may  be  found  by  using  a  clinometer  or  level  and  its 
direction  may  be  determined  with  a  compass.  The  direction  of 
dip  is  always  at  right  angles  to  the  direction  of  strike,  (Fig.  60). 
The  pitch  is  the  inclination  of  the  axis  of  a  fold  to  a  horizontal  line. 
The  pitch  and  dip  correspond  at  the  extreme  ends  of  a  pitching  anti- 
cline or  syncline,  but  in  no  other  portion  of  the  fold.  Among  miners 
the  term  pitch  usually  refers  to  the  inclination  in  the  opposite  direction 
from  that  of  the  dip.  It  may  be  expressed  as  "  up  the  dip." 


Outcrop  of  Coal  Seam 


FIG.  61. —  Stereogram  of  a  pitching  syncline  showing  the  relation  between  pitch  and 

dip  in  the  coal  seam. 

A  fold  is  a  flexure  in  rocks,  and  it  usually  consists  of  two  sections, 
the  anticline,  or  crest,  and  the  syncline,  or  trough,  of  the  wave-like 
structure.  The  axis  or  the  central  line  of  the  anticline  or  syncline  is 
never  horizontal  for  great  distances  but  bows  down  at  the  ends  in  the 
anticline  and  up  at  the  ends  in  the  syncline,  giving  pitching  anticlines 
and  synclines,  (Fig.  61).  This  explains  why  a  coal  bed  "  cropping  " 
around  the  edge  of  a  basin  forms  a  sort  of  ellipse.  Folds  may  be 
closed  or  open.  In  an  open  fold  the  limbs,  or  the  beds  on  the  sides 
of  the  flexure,  are  not  squeezed  together,  while  in  the  closed  fold  they 
are.  An  isoclinal  fold  is  one  in  which  the  limbs  are  parallel  to  each 
other.  An  overthrust  fold  is  one  in  which  the  beds  are  bent  beyond  the 
vertical  position  and  such  a  fold  may  grade  into  a  thrust  fault  where 
the  compression  becomes  sufficiently  great  to  break  the  rocks  and 
push  them  along  the  fracture.  A  monoclinal  fold  is  one  in  which 


FOLDING   IN   COAL   BEDS 


223 


the  beds  dip  in  one  direction  only  within  a  given  area.  When 
a  number  of  small,  or  secondary  anticlines  occur  on  a  large  anti- 
cline the  structure  is  known  as  an  anticlinorium,  and  if  small 
synclines  occur  on  a  large  syncline  the  resulting  structure  is  a  syn- 
clinorium. 

Folding  has  a  great  influence  on  coal  seams,  in  pinching  them  off 
as  in  horsebacks,  bulging  them  out,  and  squeezing  them  so  that  in 
some  cases  they  are  partly  turned  into  graphitic  carbon.  The  pres- 
sure is  less  in  the  crest  of  an  anticline  than  in  the  sides,  therefore  the 
coal  and  soft  rocks  like  clay  are  crowded  into  the  anticline  and  the 


FIG.  62.  —  A  sketch  by  W.  R.  Crane  of  an  anticline  in  Alaska,  in  which  the  coal  seam 
has  been  pinched  off  on  the  limbs  of  the  fold  and  crowded  into  the  crest  of  the  anti- 
cline where  the  pressure  is  least. 

seam  becomes  thicker  in  the  crest  but  thinner  on  the  limbs,  (Fig. 
62).  Where  the  folding  is  intense  there  is  always  considerable 
slipping  of  beds  over  one  another,  and  the  folds  pass  over  into  faults 
if  the  movement  becomes  intensive.  It  is  the  heavy,  strong  beds  or 
so-called  competent  beds  in  a  formation,  which  always  control  the 
folding  as  they  compel  the  softer  and  weaker  beds  to  fold  themselves 
into  such  forms  as  they  may  under  the  circumstances.  Cases  are 
even  known  where  a  certain  bed  has  been  highly  folded  although  it 
lies  between  other  beds  which  show  very  little  evidence  of  folding. 
The  latter  beds  must  have  slipped  over  each  other  and  thus  relieved 


224 


STRUCTURAL  FEATURES  OF  COAL  SEAMS 


the  pressure  without  crumpling,  while  the  former  was  compelled  to 
wrinkle  up  to  accommodate  itself  to  the  new  conditions.  An  inter- 
esting example  of  this  in  the  English  coal  fields  is  pointed  out  by 
Strahan  (Fig.  63).  This  may  have  a  bearing  on  the  origin  of  an- 
thracite in  showing  that  the  lack  of  crumpling  in  the  strata  adjacent 
to  the  coal  does  not  always  prove  the  absence  of  great  compressive 
stress  in  the  coal. 


SCA'LE  IN  FEET 


FIG.  63.  —  Contortion  in  a  parting  between  two  coal  seams  leaving  the  beds  above 
and  below  apparently  unaffected.  Tir-bach.  (After  Strahan,  Geol.  Survey  of  England 
and  Wales.) 

Faults 

A  fault  is  a  fracture  in  the  earth's  crust  along  which  the  rocks  on 
one  side  have  moved  relatively  to  those  on  the  other  side.  There  are 
three  relative  movements  which  may  occur:  (i)  The  rocks  on  one 
side  of  the  fracture  may  remain  stationary  and  those  on  the  other 
side  move  up  or  down.  (2)  Those  on  one  side  may  move  up  and  the 
others  down.  (3)  The  rocks  on  both  sides  may  move  in  the  same 
direction  but  those  on  one  side  must  move  more  than  those  on  the 
other  before  a  fault  results.  The  movement  may  also  be  along  hori- 
zontal or  oblique  rather  than  along  vertical  lines. 


FAULTS 


225 


Certain  names  are  used  to  designate  the  various  real  and  apparent 
motions  in  a  fault.  The  fracture  along  which  the  slipping  occurs  is 
usually  called  the  fault-plane  but  the  term  fault  surface  is  a  better 
word  because  the  fracture  in  many  faults  departs  widely  from  a  plane 
and  it  is  sometimes  a  regular  curved  surface.  The  term  displacement 
is  used  in  a  general  way  to  describe  the  relative  movement  of  the 
rocks  on  this  surface  whether  the  movement 
be  in  a  horizontal,  a  vertical,  or  an  oblique 
direction.  In  Fig.  64,  EF  is  the  displacement. 
The  vertical  distance  ED  the  beds  are  dis- 
placed, is  called  the  throw,  the  horizontal 
distance  FD  the  heave.  The  angle  FED, 
which  the  fracture  makes  with  the  vertical  is 
the  hade.  When  the  rocks  on  the  upthrow 
side  of  the  fracture  project  above  those  on 
the  downthrow  side  this  projection  AC  is  known  as  the  fault  scarp. 
During  the  movement  on  the  fault  surface  the  rocks  are  often  smoothed 
and  polished.  This  smooth  surface  is  a  slickenside  and  when  clay 
results  from  the  grinding  up  of  the  rocks  during  movement  it  is  called 
gouge,  or  selvage.  If  the  rocks  along  the  fracture  are  broken  up  into 
angular  fragments  the  resulting  material  is  known  as  a  fault  breccia. 

There  are  two  main  types  of  faults:     (a)  the  gravity  or  normal 
fault,  and  (b)  the  thrust  fault.     In  the  former  the  overhanging  side 


FIG.  64.  —  Diagram  illus- 
trating a  thrust  fault  and 
fault  nomenclature. 


FIG.  65.  —  Sketch  of  faults  in  main  entry  near  parting.  Southern  Coal,  Coke  and 
Mining  Co.,  Mine  No.  7,  New  Baden,  Clinton  County,  111.  (From  Bull,  of  the  111. 
Geol.  Survey,  University  of  111.  and  U.  S.  Bur.  of  Mines.) 

or  hanging  wall  side  has  moved  downward  towards  the  center  of 
the  earth  as  a  result  of  tension  or  stretching  in  the  earth's  crust,  and 
in  the  latter  the  overhanging  side  has  moved  upward  relatively  to 
the  other  side  as  a  result  of  compressive  force.  Igneous  activity 
may  sometimes  exert  an  upward  pressure  and  produce  thrust  faults. 
Figure  65  is  an  example  of  a  normal  fault  and  Figure  64  of  a  thrust 


226 


STRUCTURAL  FEATURES  OF  COAL  SEAMS 


fault.  There  are  also  various  names  used  by  the  miners  to  indicate 
the  nature  of  faults  such  as  "  shove  "  fault  and  "  slip  "  fault.  In 
the  former,  one  body  of  rock  has  been  pushed  into  another  and  the 
latter  term  is  frequently  used  for  a  fault  which  lies  nearly  parallel 
to  the  bedding. 

In  many  coal  fields  faults  are  a  source  of  great  difficulty  to  the 
miner,  but  other  fields  are  almost  entirely  free  from  them.  In  some 
faults  the  seam  is  only  thrown  a  few  feet  but  in  others  the  displace- 
ment may  be  several  thousand  feet.  Thrust  faults  show  the  greater 
maximum  displacement  and  this  may  reach  many  miles  in  the  large 
mountains.  It  may  be  considered  a  general  rule  that  the  faults  in 
any  particular  basin  will  be  practically  all  normal  or  all  thrust  unless 
it  can  be  shown  that  they  have  originated  during  at  least  two  distinct 
periods  of  faulting. 


(B) 


FIG.  66. —  Diagrams  showing  how  in  (A)  a  drill  hole  may  pass  through  the  same  coal 
seam  twice  because  of  thrust  faulting  and  in  (B)  it  may  miss  the  seam  entirely  in  the 
gap  resulting  from  normal  faulting. 

The  effects  of  faulting  on  prospecting  are  very  great.  A  concealed 
seam  may  be  brought  to  the  surface  or  a  seam  at  one  time  exposed 
may  be  faulted  and  eroded  so  that  it  no  longer  comes  to  the  surface. 
A  seam  may  be  duplicated  by  faulting  so  that  a  drill  hole  will  pass 
through  it  twice,  (Fig.  66  (A))  or  a  gap  may  be  produced  so  a  drill  will 
pass  between  the  two  portions  of  the  seam  without  indicating  its  pres- 
ence, (Fig.  66  (B)).  If  a  fault  cuts  transversely  through  a  syncline  the 
outcrops  of  the  seam  on  the  sides  of  the  syncline  after  erosion  has 
occurred  will  be  closer  together  on  the  upthrow  side  of  the  fault  than 
on  the  downthrow  side,  while  the  opposite  will  be  the  case  if  the  fault 
cuts  an  anticline. 

It  should  be  borne  in  mind  that  the  older  rocks  will  always  be  ex- 
posed on  the  upthrow  side  of  the  fault  if  the  area  has  been  eroded  since 
faulting.  In  very  few  cases  are  faults  so  recent  that  the  faulted  rocks 


UNCONFORMITIES 


227 


have  not  suffered  erosion  and  in  most  cases  all  evidence  of  the  fault 
scarp  has  been  removed.  There  is  usually,  therefore,  little  evidence 
of  the  presence  of  the  fault  on  the  surface  unless  there  be  a  marked 


FIG.  67.  —  A  large  fault  in  the  Coal  Measures  near  St.  Etienne,  France.     (Photo  by 

E.  S.  Moore.) 

difference  in  the  rocks  on  opposite  sides  of  the  fracture.  In  some 
places  a  sandstone  may  be  brought  opposite  a  shale,  a  shale  opposite 
a  limestone  or  a  non-fossiliferous  rock  may  be  brought  into  juxta- 
position to  a  fossiliferous  rock,  or 
a  sedimentary  rock  to  an  igneous 
rock.  There  are  many  features 
which  may  be  used  by  the  geologist 
to  distinguish  the  rocks  on  opposite 
sides  of  a  fault  and  thus  detect  its 
presence. 


FIG.  68.  —  Diagram  illustrating  a  great 
unconformity  by  folding,  erosion  and 
subsequent  deposition. 


Unconformities 

An  unconformity  is  an  interrup- 
tion in  the  continuous  deposition 
of  sediments  in  any  locality.  The 

presence  of  this  hiatus,  or  break  may  be  indicated  by  one  or  more  of 
a  number  of  factors  among  which  are  the  following:  (i)  A  sudden 
change  in  the  character  of  the  fossils  found  above  or  below  the 


228 


STRUCTURAL  FEATURES  OF  COAL  SEAMS 


horizon  where  the  unconformity  occurs;  (2)  Folding  or  faulting  of 
the  rocks  below  the  unconformity  while  those  above  remain  un- 
disturbed; (3)  Erosion  of  the  underlying  rocks  before  the  later  rocks 
were  laid  down  upon  them.  This  is  illustrated  in  Figure  57  where  the 
cut-out  occurs.  In  Figure  68,  the  effect  of  both  folding  and  erosion 
is  seen,  as  the  coal-bearing  formation  was  folded  and  eroded  before 
the  later  formation  was  laid  down. 

Igneous  Intrusions 

In  regions  of  igneous  activity  such  as  those  of  the  western  states, 
Alaska,  parts  of  Great  Britain  and  some  other  countries,  the  coal 
seams  have  been  cut  by  igneous  intrusions  of  many  forms.  The 


FIG.  69.  —  Diagram  illustrating  the  different  forms  which  igneous  rocks  may  assume 
in  intruding  coal  measures.  B,  a  portion  of  a  batholith;  D,  dike;  L,  laccolith;  and 
S,  sill.  Such  intrusions  produce  natural  coke  and  otherwise  alter  the  coal  adjacent 
to  them. 

different  forms  which  these  intrusions  take  are  illustrated  in  Figure  69. 
If  a  fracture  becomes  filled  with  liquid  rock  it  is  known  as  a  dike',  if 
the  liquid  spreads  out  along  a  bedding  plane  in  the  sediments  and 
solidifies  as  a  tabular  mass  of  great  areal  extent  compared  with  its 
thickness  it  is  known  as  a  sill.  If  it  forms  a  lens-shaped  body  and 
arches  up  the  overlying  strata  it  is  a  laccolith,  while  a  large,  irregular 
mass  is  a  batholith.  Other  bodies  which  have  great  vertical  dimensions 
compared  with  their  lateral,  are  known  as  bosses,  necks  or  plugs  and 


CONCRETIONARY  BODIES  IN   COAL   SEAMS 


22Q 


if  the  liquid  rock  reaches  the  earth's  surface  and  flows  out  over  the- 
surface  it  is  a  lava  flow,  or  sheet. 

Some  of  the  intrusions  in  coal  seams  are  extremely  complex  in  form. 
A  good  example  is  that  figured  by  Jukes  from  the  South  Staffordshire 
Coal  Field  in  England,  (Fig.  70).  Intrusions  of  less  complexity  may 
be  seen  in  the  Newcastle  Field  of  Australia  and  in  some  of  the  western 
states.  As  a  rule  the  dark  basic  rocks,  such  as  traps,  are  capable  of 
producing  more  complex  intrusions  than  are  the  lighter-colored,  acid 
rocks  like  granites  because  the  liquid  is  less  viscous  and  it  more  readily 
enters  intricate  fractures. 


T  =  Trap ;         C  =  Coal ;        S  =  Sandstone ; 


SCALE  20  FEET  =  1  INCH 


FIG.  70.  —  Complex  intrusion  in  coal  seam.     (After  Jukes,  Geol.   Survey  of 

England  and  Wales.) 

The  most  important  effects  of  igneous  intrusions  outside  of  the 
difficulties  they  often  create  in  mining  operations  is  the  coking  of  the 
coal.  (For  a  discussion  of  this  subject  see  Carbonite  or  Natural 
coke.)  A  dike  usually  affects  a  very  limited  area  but  a  large  sill 
or  laccolith  may  extend  for  a  long  distance  parallel  to  a  seam,  con- 
verting practically  the  whole  bed  into  coke,  as  some  of  the  sills  have 
done  in  Colorado  and  New  Mexico.  There  is  usually  a  relation  be- 
tween the  thickness  of  the  igneous  body  and  the  thickness  of  the  coked 
zone,  one  being  directly  proportional  to  the  other,  but  this  relation 
will  not  always  hold  any  more  than  it  does  in  the  case  of  the  width  of 
the  metamorphosed  zone  adjoining  intrusions  in  other  rocks.  The 
temperature  of  the  molten  rock,  its  gas  content  and  other  physical 
conditions  at  the  time  it  reaches  the  coal  have  great  influence  on  its 
coking  effects. 

Concretionary  Bodies  in  Coal  Seams 

The  concretionary  bodies  found  in  coal  and  in  the  adjacent  rocks 
commonly  go  under  the  names  of  "  coal  apples,"  "  coal  balls,"  and 


230  STRUCTURAL   FEATURES   OF   COAL   SEAMS 

"  sulphur  balls."  The  coal  apples,  or  coal  balls  consist  chiefly  of 
calcium  carbonate,  magnesium  carbonate,  iron  carbonate,  or  iron 
oxide,  with  varying  amounts  of  clay,  shale  or  sand.  Small  amounts 
of  calcium  phosphate,  carbonate  of  manganese  and  other  constituents 
are  often  present.  The  sulphur  balls  consist  of  iron  sulphide  (FeS2) 
in  the  form  of  pyrite  often  known  as  "  fool's  gold  "  or  marcasite, 
mixed  with  clay  or  sand  in  different  proportions.  In  some  cases  a 
little  free  sulphur  occurs  as  a  coating  owing  to  oxidation  of  the  pyrite. 
All  these  bodies  are  concretions  in  the  strict  sense  of  the  term.  They 
have  grown  up  as  a  result  of  the  chemical  deposition  of  these  various 
substances  around  some  central  point  and  they  show  a  concentric 
arrangement  of  the  material  varying  very  greatly  in  degree  of  perfec- 
tion. They  are  irregularly  distributed  through  the  coal  seam,  or  the 
shales  above  and  below  the  coal,  or  they  project  from  the  coal  into 
the  adjacent  rocks. 

In  addition  to  these  concretions  there  are  other  bodies  consisting 
of  coal,  which  strongly  resemble  concretions  in  appearance  but  which 
are  not  true  concretions  since  the  material  composing  them  has  not 
been  precipitated  from  solution  around  a  nuclear  point.  They  re- 
semble somewhat  the  so-called  "  physical  "  concretions  of  some  writers 
as  distinguished  from  chemical  concretions,  and  they  are  believed  to 
have  been  formed  as  a  result  of  fracturing  and  movement  in  the  bed. 
This  type  is  common  in  Colorado  where  the  coal  is  known  as  "  nigger- 
head  "  coal. 

Calcareous  concretions.  —  These  bodies  are  abundant  in  the  Coal 
Measures  where  limestones  are  associated  with  the  coal-bearing  for- 
mations. They  have  been  described  in  detail  by  S  topes  and  Watson1 
for  the  coal  fields  of  England  and  some  of  the  Continental  fields. 
They  occur  in  large  numbers  in  those  coal  seams,  the  roofs  of  which 
contain  a  marine  fauna  consisting  of  goniatites  and  lamellabranchs. 
The  waters  in  which  the  vegetal  matter  forming  the  seams  was  laid 
down  were  rich  in  salts  of  calcium  and  magnesium.  The  roof  shales 
contain  plant  remains  which  differ  considerably  from  those  in  the  coal 
seams,  thus  suggesting  that  the  vegetal  matter  in  the  overlying  rocks 
was  drifted  to  its  present  location  while  that  which  composed  the  seam 

1  Slopes,  M.  C.,  and  Watson,  D.  M.  S.,  On  the  present  distribution  and  origin  of  the 
calcareous  concretions  in  coal  seams  known  as  "coal  balls."  Phil.  Trans.  Roy.  Soc. 
London.  Series  B,  Vol.  200,  pp.  167-218,  1909. 


CALCAREOUS   CONCRETIONS 


231 


FIG.  71.  —  Vertical  dike  in  Coal  Measures,  Australia.     (Photo  by  E.  S.  Moore.) 


FIG.  72.  —  Peculiar    effects  of  shearing    in    coal.      Specimen  in  Museum  National  d' 
Histoire  Naturelle,  Paris     From  Northern  France. 


232 


STRUCTURAL   FEATURES   OF  COAL   SEAMS 


Eugene 

100  metres  North  of  Shaft  No.l 


SECTIONS  OF  THE  HOOK  OF 
EUGENE  AND  LOUIS 


Section  North  of 
Shaft  No.  1 


Louis 

400  metres  East  and 

100  metres  South  of 

Shaft  No.l 


FIG.  73.  —  Very  complicated  structures  resulting  from  faulting  and  squeezing  in  the 
coal  seams  of  Northern  France.  The  dark  areas  are  sections  of  the  seams.  (From 
the  Publications  du  Service  des  Topographies  Souterraines;  Bassin  Houiller  du 
Pas-de-Calais.) 


CALCAREOUS   CONCRETIONS  233 

grew  in  place.  This  might  be  the  result  of  the  deposition  of  plant 
remains  in  brackish  water  along  the  sea  coast  followed  by  a  trans- 
gression of  the  sea  over  this  material  with  the  deposition  of  marine 
fossils  in  calcareous  strata.  Jeffrey1  considers  that  the  coal  balls 
indicate  that  the  vegetal  matter  enclosed  in  them  was  transported 
rather  than  developed  in  situ  because  he  has  found  fragments  of  char- 
coal associated  with  other  remains  of  plants  in  the  same  concretion. 
The  material  in  the  concretions  differs  from  ordinary  coal  in  the  ab- 
sence of  the  large  proportion  of  spores  which  are  found  in  the  latter. 

These  "  coal  balls  "  almost  everywhere  contain  remarkably  well- 
preserved  plant  remains,  indicating  that  they  were  formed  about  the 
time  the  plants  settled  to  the  bottom  of  the  body  of  water  and  before 
they  had  an  opportunity  to  decompose  and  become  macerated.  It  is 
not  necessary,  as  some  writers  have  suggested,  to  invoke  the  preserva- 
tive properties  of  saline  water  to  account  for  their  preservation.  The 
perfect  sealing  conditions  provided  by  the  accumulation  of  mineral 
matter  above  the  plant  have  been  responsible  for  their  complete 
preservation,  and  the  finer  structures  of  the  plants  may  often  be  rec- 
ognized in  these  concretions  when  they  are  not  preserved  at  all  in  the 
adjacent  coal.  In  some  cases  a  plant  stem  may  extend  out  into  the 
surrounding  coal.  A  concretion  may  be  partly  in  the  coal  and  partly 
in  the  roof  slate,  and  laminations  of  the  roof  slate  may  pass  through 
some  of  the  concretions. 

Another  evidence  that  the  concretions  have  formed  early  in  the 
history  of  the  coal  seam,  in  addition  to  the  preservation  of  the  plant 
structures,  is  that  the  vegetal  matter  has  been  squeezed  down  around 
the  balls  while  they  have  been  scarcely  compressed.  They  must  have 
been  in  existence  before  the  compression  of  the  vegetal  matter  occurred, 
and  the  presence  of  slickensides  shows  that  the  coal  and  accompanying 
rocks  were  squeezed  around  them.  It  is  only  reasonable  to  suppose 
that  these  concretions  were  formed  on  the  bottom  of  the  marsh  in 
which  the  vegetal  matter  grew  and  that  they  may  have  originated 
by  the  action  of  algae  or  other  low  forms  of  plants  causing  precipitation 
of  calcium  carbonate,  as  many  calcareous  concretions  originate  at  the 
present  day.  As  they  grew,  fragments  of  plants  came  in  contact  with 
them  and  were  enclosed.  In  the  case  of  the  iron-carbonate  concre- 

1  Jeffrey,  E.  C.,  Petrified  coals  and  their  bearing  on  the  problem  of  the  origin  of  coals. 
Proc.  Nat.  Acad.  Sci.,  Vol.  3,  pp.  206-211,  1917. 


234 


STRUCTURAL   FEATURES    OF   COAL   SEAMS 


tions  it  is  possible  that  they  resulted  from  the  reaction  of  ferrous  sul- 
phate and  calcium  carbonate  in  the  presence  of  carbon  dioxide.  If 
the  supply  of  carbon  dioxide  were  insufficient,  limonite  would  have 


FIG.  74.  —  Coal  stringer,    Brilliant    Coal   and    Coke    Co.     Horn  Mine  Duquoin,  111. 
(From  the  Bull.  111.  Geol.  Survey,  University  of  111.  and  U.  S.  Bur.  of  Mines.) 

formed  instead  of  siderite  and  in  the  presence  .of  hydrogen  sulphide 
iron  pyrite  would  have  been  precipitated  to  form  sulphur  balls.  As 
to  the  agent  causing  precipitation  of  the  iron  compounds  the  iron 


1      1 

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1       1       1       1 

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I  _ 

SCALE  IN   FEET 
(T~l         2         5          4         5 

FIG.  75.  —  Roll  in  roof,  Madison  Coal  Corporation  Mine  No.  6,  Divernon,  111.     (From 
Bull.  111.  Geol.  Survey,  University  of  111.  and  U.  S.  Bur.  of  Mines.) 


bacteria  may  have  played  a  part  or  the  balls  may  be  replacements  of 
calcareous  nodules. 

In  size  these  balls  may  vary  from  minute  nodules,  less  than  an  inch 
in  diameter,  to  bodies  several  feet  in  diameter.     One  ball  about  4 


"NIGGERHEAD"    COAL  235 

feet  in  diameter  and  estimated  to  be  of  about  2  tons  weight  was  found 
in  a  mine  at  Shore,  England,  and  it  almost  completely  cut  out  the  coal 
seam.  The  balls  are  usually  roughly  spherical  and  some  large  ones 
are  made  up  of  several  smaller  concretionary  centers  cemented  to- 
gether by  carbonate  and  carbonaceous  matter. 

The  analysis  of  the  calcareous  nodules  according  to  S topes  and 
Watson  showed  calcium  carbonate  (CaC03)  as  high  as  91.09  and  as 
low  as  49.35  per  cent,  and  magnesium  carbonate  (MgCO3)  reaching 
42.82  per  cent,  thus  indicating  that  some  of  them  consist  almost  en- 
tirely of  dolomite.  Iron  pyrite  was  found  as  high  as  3.27  per  cent,  and 
other  constituents,  as  ferrous  carbonate,  ferric  oxide,  manganese 
carbonate  and  calcium  phosphate  occurred  in  small  amounts. 

The  studies  of  Zalessky1  in  the  Donetz  Basin  of  Russia  showed  that 
the  calcareous  balls  occurred  there  under  conditions  almost  identical 
with  those  described  for  England  and  northern  France.  The  coal 
seam  and  the  shales  carrying  abundant  concretions  lay  between  two 
limestones  and  the  same  types  of  plant  remains  were  preserved  in 
much  the  same  way. 

"  Niggerhead  "  coal.  —  In  the  Walsenburg  district  of  Colorado  and 
in  the  coal  fields  of  Washington  State  and  Alaska  certain  seams  of  coal 
have  been  intruded  with  igneous  rocks  and  a  great  deal  of  natural 
coke  occurs.  In  some  of  these  seams  most  of  the  coal  is  made  up  of 
roughly  spherical  masses  called  "  niggerheads,"  varying  from  an  inch 
or  less  to  a  foot  or  more  in  diameter.  They  resemble  somewhat  the 
form  taken  by  diabase  or  other  basic  rocks  on  disintegrating  by 
spheroidal  weathering.  The  laminations  in  the  coal  are  still  distinct 
in  most  of  the  balls,  and  in  many  of  them  portions  of  flat  sides  indicate 
the  original  joint  cracks,  but  the  corners  are  rounded  off  and  some  of 
the  balls  are  almost  spheres,  (Fig.  77). 

It  might  be  thought  that  these  bodies  owe  their  form  to  a  sort  of 
concretionary  development  as  a  result  of  silicification  or  other  form 
of  mineralization  of  the  coal  when  it  was  intruded  by  the  igneous 
rock,  but  the  following  analyses  show  that  it  is  not  high  in  ash  and  it 
is  considered  a  very  good  quality  of  coal  in  the  Rocky  Mountain 
fields. 

1  Zalessky,  M.  D.,  On  the  discovery  of  the  calcareous  concretions  known  as  coal  balls 
in  one  of  the  coal  seams  of  the  Carboniferous  strata  of  the  Donetz  Basin.  Bull,  de  1'ac- 
ademie  Imperiale  des  Sciences  de  St.  Petersburg,  VI  Series,  pp.  477-480,  1910. 


236  STRUCTURAL   FEATURES   OF   COAL   SEAMS 

The  subspherical  form  is  apparently  due  to  the  coal  being  heated 
to  a  high  temperature  with  the  driving  off  of  certain  volatile  matter. 


FIG.  76.  —  A  sharp  syncline  near  Hazelton,  Pa.,  from  which  the  anthracite  has  been 
removed  by  open-cut  mining.     (Photo  by  E.  S.  Moore.) 


FIG.  77.  —  "Niggerhead"  coal  from  Colorado. 

It  then  contracted  so  that  it  scales   off  concentrically  in  the  same 
manner  as  any  other  rock  which  has  been  heated  and  allowed  to  cool. 


"NIGGERHEAD"   COAL  237 

ANALYSES  OF  NIGGERHEAD   COAL  FROM  COLORADO1 


I 

ii 

in 

IV 

Fixed.  carbon 

Per  cent 

"?3    OQ 

Per  cent 

ff    2O 

Per  cent 

ri    e;i 

Per  cent 

rA    gl 

Volatile  matter     .    . 

•27    CQ 

57    78 

31    QO 

?r    Si 

M^oisture 

2    06 

2    22 

**  * 

2    D3 

Sulphur 

Q06 

.714 

714. 

742 

Ash                                  .    . 

7   3^ 

4.80 

q  8s 

6    7C 

Sp.  gr.                      ...           .    . 

1.308 

i  .  300 

I    324 

I    312 

B.t.u.  (dry). 

13,631 

13,746 

12,080 

13,12^ 

1  Analyses  furnished  through  kindness  of  D.  A.  Stout.  From  Huerfano  County, 
Colorado.  I,  Cameron  seam,  II  and  III,  Walsen  seam  and  IV,  Robinson  seam. 

There  is  also  evidence  in  the  smooth  surfaces  of  the  balls  that  consid- 
erable movement  has  occurred  between  them  and  the  adjacent  coal. 
This  may  have  resulted  from  the  great  pressure  exerted  when  the 
intrusion  entered  the  coal  seam  and  adjacent  rocks  and  it  probably 
aided  in  forming  the  rounded  bodies.  The  spherical  structure  was 
apparently  formed  after  the  coal  was  jointed  into  blocks  since  rem- 
nants of  the  joint  planes  may  still  be  seen  in  most  of  the  balls.  These 
joint  fractures  in  all  probability  aided  in  the  distribution  of  the  heat 
from  the  igneous  rocks  and  in  the  irregular  cooling  of  the  coal  when  the 
volcanic  activity  had  subsided 

The  only  other  specimen  of  coal  resembling  these  "  niggerheads  " 
from  Colorado,  which  the  writer  has  seen  was  found  in  a  seam  in  the 
Newcastle  district  of  Australia.  That  seam  had  also  been  intruded 
by  igneous  rock  and  a  spherical  mass  found  gave  unmistakable  evi- 
dence of  having  suffered  from  great  pressure  and  some  shearing.  It 
was  thought  at  the  time  to  have  been  the  result  of  pressure  squeezing 
the  more  plastic  coal  around  harder  lumps  of  the  vegetal  matter  in 
the  seam,  but  it  is  probable  that  the  heating  of  the  coal  may  also  have 
had  an  influence  in  producing  the  concretion-like  body.  A  few  speci- 
mens of  these  bodies  have  been  reported  from  the  Anthracite  field 
of  Pennsylvania  apparently  formed  by  pressure  on  the  coal. 

The  nature  of  the  origin  of  these  peculiar  bodies  does  not  seem  to  be 
fully  understood  by  mining  men  and  more  extensive  observations  re- 
garding them  are  needed. 


CHAPTER  IX 

PROSPECTING   FOR   COAL  AND   THE   VALUATION 
OF   COAL  LANDS 

Prospecting 

Prospecting  for  coal  may  be  considered  as  two  operations.  One 
of  these  is  the  search  for  coal  in  regions  where  it  has  not  already  been 
found  and  the  other  the  testing  of  geological  formations  already 
known  to  contain  at  least  some  coal. 

SEARCHING  FOR  COAL  IN  NEW  FIELDS 

Laws  governing  operations.  —  According  to  the  laws  of  the  United 
States,  coal  lands  are  classed  as  Mineral  Lands  and  unoccupied  coal 
lands  may  be  obtained  through  the  government  departments.  The 
legal  conditions  controlling  the  purchase  of  lands  already  occupied  are 
quite  different.  The  Land  Office  Regulations  relating  to  entry  on 
vacant  coal  lands  in  the  Public  Land  States  and  Territories  and  the 
district  of  Alaska  are  as  given  below,  (Sees.  2347  and  2348).  These 
were  issued  April  12,  1907  and  they  abrogate  all  previous  rules  and 
regulations  relating  to  coal  lands,1  (Sec.  2347). 

Every  person  above  the  age  of  twenty-one  years  who  is  a  citizen 
of  the  United  States,  or  who  has  declared  his  intention  to  become  such, 
or  any  association  of  persons  severally  qualified  as  above,  shall,  upon 
application  to  the  register  of  the  proper  land  office,  have  the  right  to 
enter  by  legal  subdivisions,  any  quantity  of  vacant  coal  lands  of  the 
United  States  not  otherwise  appropriated  or  reserved  by  competent 
authority,  not  exceeding  160  acres  to  such  individual  person,  or  320 
acres  to  such  association,  upon  payment  to  the  receiver  of  not  less  than 
ten  dollars  per  acre  for  such  lands,  where  the  same  shall  be  situated 
more  than  15  miles  from  any  completed  railroad  (one  constructed, 
equipped,  and  operating  on  date  of  entry),  and  not  less  than  twenty 

1  Charles  Shamel,  Mining,  mineral,  and  geological  Law.     Hill  Pub.  Co.,  1907. 

238 


LAWS   GOVERNING   OPERATIONS  239 

dollars  per  acre  for  such  lands  as  shall  be  within  15  miles  of  such  road. 
This  statute  was  authorized  March  3,  1873,  and  is  still  applicable. 
The  lands  which  may  be  entered  must  be  surveyed  and  legally  sub- 
divided, they  must  contain  workable  coal  deposits,  but  they  must  not 
contain  valuable  deposits  of  gold,  silver,  or  copper. 

Coal  lands  may  also  be  entered  according  to  the  following  statute 
(Sec.  2348)  on  the  basis  of  a  preference  right  to  purchase:  Any 
person  or  association  of  persons  severally  qualified  (as  provided  in 
Sec.  2347),  who  have  opened  and  improved,  or  shall  hereafter  open 
and  improve,  any  coal  mine  or  mines  upon  the  public  lands  and  shall 
be  in  actual  possession  of  the  same,  shall  be  entitled  to  a  preference 
right  of  entry  under  the  preceding  section  (Sec.  2347)  of  the  mines 
so  opened  and  improved :  Provided,  that  when  any  association  of  not 
less  than  four  persons  severally  qualified  as  above  provided  shall  have 
expended  not  less  than  five  thousand  dollars  in  working  and  im- 
proving any  such  mine  or  mines,  such  association  may  enter  not  ex- 
ceeding 640  acres,  including  such  mining  improvements.  To  preserve 
a  preference  right  the  person  or  association  must  present  to  the  register 
of  the  proper  land  district,  within  sixty  days  from  the  date  of  actual 
possession  and  commencement  of  improvements  a  declaratory  state- 
ment therefor,  in  all  cases  when  the  township  plot  has  been  filed. 

An  individual  or  the  several  individuals  of  an  association  are  en- 
titled to  but  a  single  entry  on  coal  lands.  No  one  can  operate  or 
work  a  coal  mine  for  profit  upon  the  public  lands  without  having 
made  the  proper  entry. 

Those  desiring  information  regarding  public  coal  lands  should 
apply  to  the  register  of  a  land  district,  who  is  furnished  from  time  to 
time  with  schedules  and  maps.  These  maps  show  three  types  of 
lands:  (i)  Those  lands  known  to  lie  outside  of  ascertained  coal  areas 
and  open  to  entry  under  the  general  land  laws.  (2)  Those  lands 
known  to  contain  workable  deposits  of  coal,  whereon  prices  will  be 
fixed  upon  information  derived  from  field  examination.  (3)  Those 
lands  containing  coal  of  such  character  as  may  from  their  location 
with  reference  to  transportation  lines,  be  sold  at  the  minimum  price 
fixed  by  statute.  The  lands  of  the  first  and  third  types  are  entered 
at  minimum  prices  as  stated  above  and  those  of  the  second  type  at 
prices  fixed  in  the  schedules. 


240  PROSPECTING  AND   VALUATION  OF  COAL  LANDS 

Entry  on  coal  lands  in  Alaska:  To  make  entry  on  unreserved 
coal  lands  in  Alaska1  the  same  individual  and  personal  qualifications 
are  necessary  as  in  the  United  States  but  entry  may  be  made  on  un- 
surveyed  coal  lands.  In  unsurveyed  tracts  the  lands  upon  which  a 
mine  or  mines  are  situated  must  be  located  in  rectangular  tracts  of 
40,  80,  or  1 60  acres  with  north  and  south  boundary  lines  run  accord- 
ing to  the  true  meridian  and  marked  by  permanent  monuments. 
All  locators  shall  within  one  year  of  making  a  location  file  a  notice 
with  the  register  of  the  land  district. 

To  obtain  a  patent  an  application  for  such  must  be  filed  with  the 
register  and  receiver  of  the  land  district  within  three  years.  A  patent 
gives  control  of  the  land  to  the  patentee  and  his  heirs. 

The  regulations  governing  the  control  of  coal  deposits  in  lands 
other  than  the  Public  Lands  of  the  United  States  vary  with  different 
states.  In  many  states  the  person  holding  land  in  fee  also  holds  the 
minerals  lying  beneath  the  surface  unless  they  have  been  expressly 
reserved  in  the  deed.  In  others,  such  as  Wyoming  and  Colorado, 
the  coal  land  is  leased  only  on  a  royalty  basis. 

The  recent  leasing  law  for  coal  lands:  On  February  25,  1920,  the 
President  of  the  United  States  signed  an  act  known  as  an  "  Act  to 
promote  the  mining  of  coal,  phosphate,  oil,  oil  shale,  gas  and  sodium 
on  the  public  domain."  This  bill  places  the  development  of  these 
lands,  not  including  those  of  Alaska,  under  the  control  of  the  Secretary 
of  the  Interior  and  it  throws  open  millions  of  acres  of  coal  and  oil 
lands  in  the  West  for  leasing  purposes.  The  law  refers  to  lands 
classified  or  unclassified  but  it  does  not  include :  (a)  Lands  in  .National 
parks;  (b)  Lands  controlled  by  the  Appalachian  Forest  Reserve  Act; 
(c)  Lands  in  military  or  naval  reservations;  (d)  Indian  reservations; 
(e)  Ceded  or  restored  Indian  lands  the  proceeds  of  which  are  credited 
to  the  Indians. 

According  to  this  act  coal  lands  may  be  leased  to  citizens,  asso- 
ciations of  citizens,  corporations,  and  municipalities  in  tracts  of  40 
acres  or  multiples  thereof  up  to  2560  acres  by  one  applicant.  The 
tracts  are  to  be  contiguous  if  possible  for  them  to  be  so.  Railroads 
may  work  for  their  own  use  for  railroad  purposes  only  one  grant  for 

1  Regulations  governing  Coal  Land  Leases  in  the  Territory  of  Alaska.  Dept.  of  the 
Interior,  Washington,  May  18,  1916. 


LAWS   GOVERNING  OPERATIONS  241 

each  200  miles  of  road.  There  is  to  be  paid  to  the  Government  a 
royalty  on  coal  leases  of  not  less  than  5  cents  a  ton  (2000  Ibs.)  and  a 
yearly  rental  of  not  less  than  25  cents  an  acre  for  the  first  year,  not 
less  than  50  cents  an  acre  for  the  second  to  the  fifth  year  inclusive, 
and  not  less  than  $1.00  an  acre  for  the  remainder  of  the  term  of  the 
lease.  Leases  are  for  indeterminate  periods  not  to  exceed  twenty 
years  but  renewable  to  a  like  extent.  In  an  emergency  individuals  or 
associations  may  be  allowed  to  mine  coal  for  their  own  domestic  use 
without  payment  of  rent  or  royalty.  This  privilege  is  restricted  to  an 
area  of  40  acres  and  a  license  of  two  years  duration.  Municipalities 
may  lease  coal  lands  for  their  own  use  without  the  payment  of  rent 
or  royalty  under  the  following  special  conditions:  The  coal  must 
be  used  for  domestic  purposes  only,  which  means  household  purposes; 
a  municipality  of  less  than  100,000  population  is  limited  to  an  area 
not  exceeding  320  acres,  one  of  100,000  to  150,000  population  to  an 
area  not  exceeding  1280  acres  and  one  of  a  population  of  over  150,000 
is  limited  to  an  area  not  exceeding  2560  acres.  The  special  lease 
granting  this  privilege  is  limited  to  four  years. 

No  person,  association  or  corporation,  except  as  provided,  shall 
have  more  than  one  coal,  phosphate  or  sodium  lease  during  the  life 
of  such  lease  in  any  one  state.  "  No  person  or  corporation  shall  take 
or  hold  any  interest  or  interests  as  a  member  of  an  association  or 
associations  or  as  a  stockholder  of  a  corporation  or  corporations  hold- 
ing a  lease  under  the  provisions  of  this  bill  which  together  with  the 
area  embraced  in  any  direct  holding  of  a  lease  under  this  Act  or  which 
together  with  any  other  interest  or  interests  as  a  member  of  an  associa- 
tion or  associations  or  as  a  stockholder  of  a  corporation  or  corporations 
holding  a  lease  under  the  provisions  hereof,  for  any  kind  of  mineral 
leased  hereunder,  exceeds  in  the  aggregate  an  amount  equivalent  to  the 
maximum  number  of  acres  of  the  respective  kinds  of  minerals  allowed 
to  any  one  lessee  under  this  Act.  Any  interests  held  in  violation  of 
this  Act  are  forfeited  to  the  United  States." 

Permits,  known  as  coal  prospecting  permits  may  be  granted,  which 
gives  the  holder  the  exclusive  right  to  prospect  unclaimed  and  un- 
developed lands  where  exploratory  work  is  necessary  to  determine 
the  existence  or  workability  of  coal  deposits.  These  permits  cover 
a  maximum  area  of  2560  acres  and  they  are  good  for  two  years. 


,.- 


242  PROSPECTING  AND   VALUATION  OF   COAL  LANDS 

CRITERIA  FOR  LOCATING  NEW  SEAMS  OR  KNOWN  SEAMS 
IN  NEW  AREAS 

In  looking  for  new  seams  of  coal  there  are  certain  conditions  which 
should  govern  the  prospector's  operations.  A  seam  may  outcrop 
at  the  surface  but  if  the  adjacent  rocks  have  suffered  much  disin- 
tegration very  little  definite  evidence  of  the  coal  may  be  found  with- 
out excavating.  There  may  often  be  found  a  black  band,  or  area, 
known  as  the  "  smut  "  or  "  blossom  "  which  indicates  the  position 
of  the  seam.  In  some  cases  the  presence  of  a  seam  which  is  covered 
with  clay  or  sand  wash  may  only  be  inferred  by  finding  minute  frag- 
ments of  the  coal  mixed  with  the  sediment  carried  down  grade  by 
water  or  transported  in  a  certain  direction  by  a  glacier.  Outcrops 
are  most  frequently  found  in  gullies  and  ravines  and  quite  frequently 
seepages  or  springs  of  water  in  the  bank  indicate  the  position  of  seams 
of  coal. 

In  prospecting  it  should  be  observed  that  coal  is  only  found  in 
stratified  rocks,  and  it  is  absolutely  useless  to  search  for  it  in  those 
of  igneous  origin.  Further,  of  the  stratified  rocks,  there  are  usually 
certain  types  which  carry  the  coal.  These  are  shales,  or  slates  de- 
rived from  the  shales,  and  sandstones.  Black  shales  are  the  most 
favorable.  Although  coal  has  been  found  in  limestones,  it  is  very 
rarely  indeed  that  it  is  found  in  a  limestone  formation  in  which  there 
is  not  also  considerable  shale  or  sandstone,  and  there  is  no  chance 
of  finding  it  in  quantities  in  distinct  limestone  formations.  Regard- 
ing sandstones  and  conglomerates,  the  latter  rarely  carry  coal  except 
along  shaly  and  sandy  bands.  Clean  sandstones  are  poor  coal- 
bearers  as  most  of  the  coal  in  sandy  rocks  is  found  in  impure  sand- 
stone containing  clay  or  in  feldspathic  sandstones  known  as  arkoses. 

Although  shales  and  impure  sandstones  are  favorable  rocks  for  the 
occurrence  of  coal  not  all  of  them  carry  it.  In  America  no  coal  has 
been  found  in  rocks  older  than  those  of  the  Mississippian,  or  Lower 
Carboniferous  series,  but  in  Europe  a  little  has  been  found  in  rocks 
as  old  as  the  Devonian.  Carbonaceous  shales  may  be  found  as  low  as 
the  Archean  rocks,  but  the  geological  and  botanical  conditions  had 
not  become  favorable  for  the  formation  of  coal  before  the  periods 
mentioned  above.  There  are  many  examples  of  people  spending 
large  sums  of  money  in  drilling  in  these  older  formations,  as  for  ex- 


CRITERIA  FOR  LOCATING  NEW   SEAMS  243 

ample,  in  the  Ordovician  black  shales,  where  there  is  no  possibility 
of  finding  coal.  There  is  good  evidence  to  show  that  the  great  groups 
of  land  plants  which  gave  rise  to  the  coal  had  not  developed  before 
the  Devonian  period,  and  in  America  as  well  as  in  some  of  the  other 
continents  the  sea  covered  so  much  of  the  continent  that  there  was 
little  opportunity  for  coal  to  form  in  the  Devonian. 

The  coal-bearing  formations  are  found  principally  in  the  Carbon- 
iferous, Cretaceous,  and  Tertiary  systems.  There  is  a  little  coal  in 
the  Jurassic  in  Alaska,  and  outside  of  America  the  Jurassic  and  Tri- 
assic  coals  are  important.  In  dividing  these  systems  of  rocks  into 
smaller  divisions  so  that  certain  seams  of  coal  may  be  located  or  a 
seam  may  be  traced  from  one  basin  to  another  the  different  plant 
fossils  may  be  used  to  correlate  beds,  and  animal  fossils  in  the  ad- 
jacent rocks  often  serve  to  identify  the  seams.  Thiessen  claims  to 
have  discovered  from  his  microscopic  studies  that  the  plant  spores 
found  in  any  coal  seam  have  characters  distinct  from  those  of  spores 
in  other  seams,  and  may  be  used  as  a  determinative  factor  in  recog- 
nizing the  seam  in  various  localities.  This  new  evidence  of  the  dif- 
ference in  the  spores  from  different  seams  is  likely  to  be  of  considerable 
practical  value  in  the  future  in  correlating  seams. 

In  addition  to  the  fossils  there  are  often  other  features  which 
locally  distinguish  one  seam  from  another,  such  as  the  presence  of 
"  sulphur  balls  "  or  other  concretions  in  some  seams  and  their  ab- 
sence in  others,  the  fracture  of  the  coal,  the  presence  of  streaks  of 
cannel  or  mineral  charcoal,  the  nature  of  the  adjacent  rocks  and 
similar  features.  The  adjacent  rock  may  be  a  fire  clay,  a  calcareous 
rock  or  some  distinctive  sandstone  which  can  be  recognized  wherever 
met. 

Testing  coal-bearing  formations  to  determine  the  extent  of  the 
seams.  —  A  coal  seam  may  vary  greatly  in  thickness  within  very 
short  distances  or  it  may,  like  the  Pittsburgh  seam  of  the  Appalachian 
province,  extend  with  a  fairly  uniform  thickness  over  several  thous- 
and square  miles.  Shallow  seams  may  be  tested  with  tunnels,  pits, 
or  shafts,  but  where  they  lie  much  below  the  surface  prospecting  is 
usually  done  with  a  core  drill.  The  diamond  drill  is  most  commonly 
used,  although  a  rotary  calyx  drill  has  also  been  employed.  The 
advantage  in  using  drills  of  this  type  is  in  the  core  which  is  obtained. 

As  few  coal  seams  lie  horizontally  the  length  of  the  section  of  coal 


244  PROSPECTING  AND   VALUATION  OF   COAL   LANDS 

in  the  drill  core  from  any  seam  will  depend  upon  the  angle  at  which 
the  hole  perforates  the  seam  and  will  vary  inversely  as  the  acute  angle 
for  a  vertical  hole.  If  the  hole  be  vertical,  the  angle  will  be  found  by 
subtracting  the  angle  of  dip  of  the  bed  from  90°,  that  is,  the  angle 
will  be  the  complement  of  the  angle  of  dip.  In  case  the  hole  is  not 
vertical  but  is  still  in  a  plane  normal  to  the  strike,  the  angle  which  it 
makes  with  the  seam  can  be  found  by  subtracting  the  angle  of  dip 
from  90°  and  then  adding  the  angle  the  hole  makes  with  the  vertical, 
if  it  be  inclined  in  the  opposite  direction  to  the  seam,  or  subtracting 
it,  if  it  be  inclined  in  the  same  direction.  These  figures  may  be  easily 
obtained  by  use  of  a  clinometer. 

If  the  hole  is  driven  so  that  it  departs  from  the  vertical  in  a  plane 
which  is  parallel  to  the  strike  and  therefore  normal  to  the  dip,  the 
difference  between  the  true  thickness  of  the  seam  and  the  thickness 
shown  in  the  core  will  increase  as  the  angle  which  the  hole  makes  with 
the  vertical  increases. 

In  the  case  of  holes  drilled  at  an  angle  to  the  vertical  and  lying  in 
any  other  plane  than  the  plane  parallel  to  the  direction  of  strike  of 
the  seam  or  in  the  plane  normal  to  the  strike,  as 
mentioned  above,  the  conditions  become  quite  com- 
plicated and  must  be  worked  out  for  each  individual 
case. 

In  all  the  cases  mentioned  above,  the  true  thickness 
of  the  seam  may  be  determined  from  the  thickness 
of  coal  in  the  core  by  a  solution  of  the  triangles  in- 
]D  volved,  but  the  simplest  method  and  one  sufficiently 
accurate  for  all  practical  purposes  is  to  solve  the 
]B  problem  graphically.     This  is  done  as  follows:     In 
FIG.    78.  —  Graphic  Figure  78  let  A  B  be  a  drill  core  containing  a  band 
method  of  deter-  of  coai  CD.     Carefully  project  the  coal  seam,  keeping 
mining  the  thick-  ^  inclination,  and  draw  a  line  from  A  per- 

ness  of  a  coal  seam 

from  the  drill  core,  pendicular  to  the  projected  seam.  The  distance  EF 
will  bear  the  same  relation  to  the  distance  CD 
(which  is  already  known)  that  the  true  thickness  of  the  seam  does 
to  the  thickness  of  the  coal  in  the  core  since  they  are  drawn  to  the 
same  scale.  If  CD  be  10  feet  and  EF  scales  half  as  much  as  CD 
the  true  thickness  of  the  seam  will  therefore  be  5  feet. 


DETERMINATION  OF   THICKNESS   OF   COAL   FORMATIONS       245 


Determination  of  thickness  of  ccal  formations.  —  There  are  several 
means  of  determining  the  thickness  of  an  outcropping  coal  seam  or 
of  a  formation  containing  one  or  more  seams,  without  the  use  of  the 
drill.  The  method  employed  depends  upon  the  circumstances,  (i) 
If  the  beds  lie  flat  and  are  exposed  in  a  cliff  (a)  the  vertical  height  of 
the  cliff  will  be  the  thickness.  (2)  If  the  beds  dip  there  may  be  sev- 
eral different  conditions:  the  surface  may  be  level  where  the  for- 
mation outcrops  (b) ;  the  rocks  may  outcrop  in  a  slope,  which  is  inclined 
in  a  direction  opposite  to  the  direction  of  the  dip  of  the  strata  (c) ; 
the  rocks  may  outcrop  in  a  slope  which  is  inclined  in  the  same  direction 
as  the  dip  of  the  strata,  (d)  (Fig.  79).  The  thickness  of  the  formation 


FIG.  79.  —  Determination  of  the  thickness  of  a  formation  under  varying  conditions. 

is  found  by  solving  the  triangles  in  the  three  cases,  (b),  (c),  and  (d) 
as  follows:  (b)  Since  the  angle  of  dip  ACB  and  the  distance  CA  may 
be  measured,  the  distance  AB  is  easily  found  from  the  formula. 


Sin  ACB  =         ,  or  AB  =  CA  Sin  ACB,  (c)  AB  =  CA  Sin  (ACD  -f 

O^T. 

DCB).  The  slope  distance  and  angle  of  dip  are  measured  and  the 
angle  of  slope  ACD  may  either  be  measured  or  found  from  its  sine, 
computed  from  the  length  of  the  slope  and  the  difference  in  elevation. 
(d)  AB  =  CA  sin  (DCB  -  DC  A). 

As  the  angle  of  dip  increases  the  horizontal  distances  normal  to  the 
strike  approach  more  nearly  the  thickness  of  the  formation  until  the 
dip  becomes  90°,  or  vertical,  and  the  two  are  then  equal. 

Graphic  method:  The  thickness  of  a  series  may  be  very  conveniently 
and  rapidly  determined  by  the  graphic  method  when  the  angle  of  dip 
and  the  horizontal  distance  across  the  outcrop  are  known,  (Fig.  80). 
In  this  diagram  the  numbers  on  the  left  hand  side  of  the  diagram  repre- 
sent various  dip  angles  and  each  vertical  space  corresponds  to  any 
chosen  unit  of  measurement.  To  determine  the  thickness  find  the 
number  corresponding  to  the  number  of  degrees  in  the  dip  angle  and 
follow  the  horizontal  line  to  the  right  for  as  many  units  as  there  are 


246 


PROSPECTING  AND   VALUATION   OF   COAL   LANDS 


in  the  distance  across  the  outcrop.  Then  follow  the  curved  line  (or 
an  imaginary  curved  line  between  two  of  the  curved  lines  if  the  point 
falls  between  two  lines)  to  the  top  of  the  figure  and  count  the  number 
of  units  between  the  point  reached  and  the  left  margin.  The  vertical 
spaces  may  each  be  taken  as  equal  to  5,  10,  20,  100,  1000,  or  any  other 
number  of  feet,  the  same  scale  being  used  in  all  parts  of  the  diagram 


10° 


FIG.  80.  —  Diagram  employed  in  the  graphic  determination  of  the  thickness  of  geological 
formations.     (After  Hayes.) 

in  any  one  calculation.  To  illustrate  its  use:  Let  a  formation  out- 
cropping on  a  level  surface  dip  30°  and  the  distance  across  its  outcrop 
normal  to  the  strike  be  1000  feet.  Its  thickness  is  found  by  following 
the  horizontal  line  from  30°  to  the  right  and  if  each  vertical  space  be 
considered  equal  to  100  feet,  the  point  corresponding  to  1000  feet  will 
fall  on  the  fifth  curved  line.  If  this  line  be  followed  to  the  top  of  the 
diagram  and  the  same  scale  be  used,  it  will  be  found  that  the  distance 
to  the  left  margin  is  500  feet.  Instead  of  considering  each  space 


DETERMINATION   OF   DEPTH   OF   COAL   SEAM  247 

equivalent  to  100  feet  another  scale  might  have  been  used,  for  example 
200  feet  or  50  feet  per  space.  It  is  best  in  all  cases  to  use  as  small  a 
number  of  feet  to  a  space  as  the  diagram  will  permit  in  order  to 
minimize  the  error  in  computing  the  thickness.  In  this  connection 
it  is  sometimes  wise  to  use  a  certain  fraction  of  the  distance  across  the 
outcrop  to  obtain  the  thickness  of  that  fraction  of  the  formation,  and 
then  to  find  the  total  thickness  from  this  fraction.  For  example  the 
total  distance  across  the  outcrop  of  the  formation  is  2000  feet.  In 
order  to  use  a  large  scale  on  the  diagram  find  the  thickness  corre- 
sponding to  a  distance  of  200  feet  and  multiply  this  by  10,  to  find  the 
thickness  for  the  whole  formation. 

In  addition  to  the  methods  suggested  above,  the  thickness  of  a 
formation  may  be  determined  graphically  by  simply  drawing  to  scale 
diagrams  like  those  in  Figure  79,  and  scaling  off  the  distance  repre- 
senting the  thickness.  If  this  is  done  carefully  and  on  a  fairly  large 
scale  the  results  will  be  satisfactory  for  most  purposes  since  in  most 
cases  thicknesses  and  dips  are  subject  to  considerable  variation  within 
short  distances. 

Determination  of  the  depth  of  a  coal  seam  at  different  points.  - 
If  an  outcropping  seam  lies  flat  its  depth  below  the  surface  at  any 
point  can  readily  be  found  from  the  topographic  map.  On  many 
geological  maps  structural  contour  lines  are  drawn  on  one  important 
seam  in  a  coal-bearing  formation  and  all  points  on  any  one  of  these 
lines  have  the  same  elevation  above  sea  level.  These  contours  bring 
out  the  subterranean  topography  and  the  structural  features  of  the 
seam  and  when  they  are  placed  on  a  topographic  map  the  depth  of 
the  seam  at  any  point  is  quickly  found  by  taking  the  difference  be- 
tween the  elevation  of  the  surface  at  that  point  as  shown  on  the  top- 
ographic map  and  the  contour  line  on  the  seam  lying  beneath  this 
point,  (Fig.  81). 

When  an  outcropping  seam  dips  it  may  be  desired  to  find  its  depth 
at  certain  points  at  various  distances,  and  in  various  directions  from 
some  point  on  the  outcrop.  For  convenience  in  discussion,  the 
depth  of  a  seam  in  three  directions  from  a  point  on  the  outcrop  and 
at  varying  distances  from  that  point  will  be  considered.  The  con- 
ditions are  illustrated  by  Fig.  82.  Let  A  BCD  represent  a  section 
of  a  seam  outcropping  along  AB.  The  direction  of  strike  is  parallel 
to  AB  and  the  direction  of  dip  normal  to  AB  and  parallel  to  PM. 


248 


PROSPECTING  AND   VALUATION  OF  COAL  LANDS 


100 


FIG.  81.  —  Relation  between  surface  contours  and  structural  contours  drawn  on  the 
surface  of  a  coal  seam  underground.  The  former  are  the  light  lines  and  the  latter 
the  heavy  ones. 


/                                     M 

/'I,'           JM           X 

j  /             \  1 

II 

''         i 

II 

\( 

/                  \ 

H 

,                    \ 

H 

;X                                   \ 

II 

; 

' 

/                     \ 

" 

,                      \ 

i 

1 

i 

FIG.  82.  —  Diagram  illustrating   the   determination   of   the    depth  of  a  coal  seam  at 
varying  distances  and  in  different  directions  from  a  point  on  the  outcrop. 


DETERMINATION  OF  DEPTH  OF  COAL  SEAM 


249 


(i)  In  the  first  case  consider  the  depth  of  the  seam  below  various 
points  L,  O,  and  M,  along  a  line  parallel  to  the  dip.  The  angle  of 
dip,  MPN  and  the  distances  PL,  PO,  or  PM  being  measured,  the 
depth  is  found  from  the  tangent  of  the  angle  of  dip.  It  is  seen  that 
the  depth  at  any  point  will  be  directly  proportional  to  the  distance 
from  the  point  P,  and  the  following  table  shows  the  depth  of  a  seam 
at  points  10  feet  from  a  point  on  the  outcrop  when  measured  on  a 
horizontal  surface,  supposing  the  seam  dips  at  various  angles  from  5° 
to  85°.  At  90°  the  bed  is  vertical.  To  find  the  depth  of  the  seam 
beneath  any  other  point  along  this  line  multiply  the  number  given  in 
the  table  by  the  distance  in  feet  and  divide  the  result  by  10. 

TABLE   SHOWING  THE  DEPTH   OF  A  COAL  SEAM  AT  VARIOUS 

DISTANCES  IN   DIRECTION   OF  DIP  FROM  THE  OUTCROP, 

FOR  DIFFERENT  ANGLES  OF   DIP 


Angle  of  dip 

10  feet  from  outcrop 

Angle  of  dip 

10  feet  from  outcrop 

5° 

.8749  feet 

50° 

11.918  feet 

10 

I-7633 

55 

14.281 

15 

2.6795 

60 

17.321 

20 

3.6397 

65 

21-445 

25 

4-6631 

70 

27-475 

30 

5-7735 

75 

37-321 

35 

7.0021 

80 

56.713 

40 

8.3910 

85 

114.300 

45 

IO.OOOO 

(2)  In  the  second  case  consider  the  depth  at  various  points  along 
a  line  45°  from  the  direction  of  dip.  Or  in  the  diagram  (Fig.  82) 
let  the  direction  of  the  dip  be  south,  the  strike  east  and  west,  and  the 
direction  (PH)  under  consideration,  southeast.  On  this  line,  PH 
the  depth  at  any  points  such  as  E,  F,  and  H,  will  be  found  by  first 
measuring  the  distance  PE,  PF,  or  PH,  then  drawing  a  line  from 
this  point  normal  to  the  line  PM  meeting  PM  at  the  point  K.  The 
triangle  PFK  thus  formed  is  solved,  PK  is  found  and  the  problem 
then  becomes  the  same  as  that  described  above  for  the  first  case  con- 
sidered. The  following  table  shows  the  depth  of  a  seam  at  points 
10  feet  from  a  point  on  the  outcrop,  measured  for  various  dips  of 
5°-85°  in  a  direction  45°  from  the  direction  of  dip. 

To  obtain  the  figures  for  any  other  point,  multiply  by  the  distance 
in  feet  and  divide  by  10. 


250 


PROSPECTING  AND   VALUATION   OF  COAL  LANDS 


TABLE   SHOWING  DEPTH   OF  A   SEAM  AT   POINTS  ALONG  A 

LINE  45°  FROM   DIRECTION   OF   DIP  FOR  VARIOUS 

ANGLES   OF   DIP 


Angle  of  dip 

10  feet  from  outcrop 

Angle  of  dip 

10  feet  from  outcrop 

5° 

.61855  feet 

50° 

8.42602  feet 

10 

i  .  24665 

55 

10.09666 

15 

1.89440 

60 

12.24594 

20 

2.57326 

65 

15.16161 

25 

3-29681 

70 

19.42482 

30 

4.08176 

75 

26.38594 

35 

4.95048 

80 

40.09609 

40 

5.93243 

85 

80.81010 

45 

7  .07110 

The  formula  for  determining  the  depth  D  at  a  point  C  feet  from  the 
outcrop  and  in  a  direction  at  A°  to  the  direction  oi  dip,  if  the  angle 
of  dip  be  B°,  is 

D  =  Tan.     B  x  C  cos  A. 

An  instrument  known  as  Brunton's  slope  chart  is  a  convenient  ap- 
paratus for  determining  the  apparent  dip  of  the  bed  at  any  angle 
of  divergence  from  the  true  dip.  It  is  for  the  purpose  of  mechanic- 
ally solving  the  formula  Tan  C°  =  Sin  A  °  Tan  B°,  where  A  is  the  angle 
of  divergence  from  the  true  dip,  B  the  true  dip,  and  C  the  apparent 
dip.  Thus,  after  the  angle  C  has  been  found,  the  depth  at  any  point 
is  found  just  as  in  the  case  where  the  measurement  is  taken  along  the 
true  dip  by  finding  the  tangent  of  C  and  using  the  table  given  for  the 
first  case. 

(3)  In  the  third  case  it  should  be  observed  that  any  point  along  the 
line  of  strike  of  a  coal  seam  will  be  at  the  same  depth  as  every  other 
point  on  that  line  whether  the  seam  be  considered  at  the  surface  or 
at  the  bottom  of  a  mine  shaft.  This  is  evident  since  the  strike  is  the 
line  along  which  the  seam  intersects  a  horizontal  plane. 

The  Valuation  of  Coal  Lands 

Factors  governing  the  value.  —  The  chief  factors  which  influence 
the  value  of  coal  lands  are :  (a)  the  proximity  of  the  coal  to  an  impor- 
tant market  center;  (b)  the  transportation  facilities;  (c)  the  abundance 
or  scarcity  of  coal  in  the  district;  (d)  the  nature  of  the  coal;  (e)  the 
depth  at  which  it  occurs;  (/)  the  thickness  of  the  seam;  and  (g)  the 


DEPTH   OF   COAL  MINE   SHAFTS   IN   UNITED    STATES  251 

other  geological  conditions  which  affect  mining  operations,  such  as 
folded  or  faulted  strata,  abundance  of  water  and  the  character  of 
the  floor  and  roof  of  the  seam.  -The  nearness  of  coal  deposits  to  a 
good  market  may  be  offset  by  labor  difficulties  and  poor  quality  of  the 
coal  or  the  difficulty  of  mining  it,  while  the  handicap  of  being  a  con- 
siderable distance  from  the  market  may  be  overcome  by  good  trans- 
portation facilities,  especially  by  water,  and  the  favorable  condition 
of  most  of  the  other  factors  mentioned.  If  there  be  little  fuel  in  the 
vicinity  of  a  large  city  the  lower  grades  of  coal,  such  as  lignite,  may 
bring  a  good  price  whereas  they  would  scarcely  be  used  if  there  were 
plenty  of  good  bituminous  coal  or  anthracite  in  the  region.  Good 
gas  coal  is  in  demand,  especially  around  cities,  and  high-grade  coking 
coal  is  much  sought  after  for  metallurgical  purposes.  If  it  occurs  in 
large  amounts,  industrial  centers  may  grow  up  in  areas  where  it  is 
found. 

THE  MAXIMUM  DEPTH  OF  COAL  MINES 

The  depth  of  coal  mine  shafts  in  the  United  States.  —  In  the 

United  States  it  is  customary  to  regard  any  coal  lying  below  3000 
feet  as  negligible  in  estimating  the  value  of  the  land,  because  industrial 
conditions  make  it  impossible  at  present  to  mine  the  coal  profitably 
at  a  greater  depth.  It  is  the  consensus  of  opinion,  however,  that  the 
time  is  not  far  distant  when  the  maximum  depth  for  profitable  mining 
will  be  extended  to  at  least  4000  feet,  as  this  depth  is  almost  attained 
in  Belgium  at  the  present  time,  and  in  England  for  almost  half  a  century 
all  seams  less  than  4000  feet  deep  have  been  figured  in  the  reserves. 
There  are  no  mechanical  impediments  to  mining  at  that  depth  or 
even  at  a  much  greater  depth;  but  the  abundance  of  coal,  the  high 
cost  of  labor  and  the  low  price  which  usually  prevails  in  the  United 
States  when  compared  with  prices  in  those  countries  where  deep  min- 
ing is  carried  on  make  it  impossible  to  mine  coal  profitably  at  these 
great  depths  in  this  country. 

The  maximum  depths  at  which  coal  is  mined  at  the  present  time 
in  the  various  fields  of  this  country  are  approximately  as  follows:1 
The  deepest  mining  is  in  the  anthracite  region  of  Pennsylvania,  and 
it  reaches  about  2200  feet  although  the  deepest  shaft  is  only  1850  feet. 

1  Fisher,  C.  A.,  Depth  and  minimum  thickness  of  coal  beds  as  limiting  factors  in  valu- 
ation of  coal  lands.  U.  S.  Geol.  Survey,  Bull.  424,  p.  48,  1910. 


252  PROSPECTING  AND   VALUATION   OF  COAL   LANDS 

This  depth  does  not  indicate  the  maximum  depth  of  the  coal  in  the 
anthracite  region  as  the  depth  of  a  few  of  the  basins  has  not  yet  been 
determined  and  from  every  indication  it  is  very  great.  In  the  not 
far  distant  future  it  is  probable  that  coal  will  be  mined  from  the 
Southern  Field  at  a  depth  of  at  least  3500  feet.  In  the  Schuylkill 
section  the  coal  probably  reaches  4500  feet  or  more  in  depth. 

In  the  bituminous  fields  of  the  Appalachian  province  the  coal  does 
not  lie  at  great  depths  in  many  places,  the  deepest  so  far  known  being 
in  Alabama  where  some  of  it  exceeds  3000  feet.  The  deepest  shafts 
are  not  over  1000  feet  in  the  states  of  Pennsylvania,  Ohio,  West 
Virginia,  eastern  Kentucky,  Tennessee,  and  Alabama,  and  there  are 
large  areas  where  all  shafts  are  less  than  200  feet  in  depth. 

In  the  Eastern  Interior  field,  including  Illinois,  Indiana,  and  western 
Kentucky,  the  greatest  depth  reached  is  at  a  mine  in  Illinois,  which 
is  slightly  over  1000  feet,  but  most  of  the  coal  in  these  states  is  com- 
paratively shallow.  In  Michigan  the  seams  lie  very  close  to  the  sur- 
face and  the  shafts  are  seldom,  if  ever,  more  than  200  feet  deep. 

In  the  Western  Interior  field  the  depth  reached  in  Iowa,  Missouri, 
and  northeastern  Kansas  scarcely  exceeds  300  feet,  while  in  eastern 
Kansas,  Oklahoma,  and  western  Arkansas  the  depth  is  considerably 
greater.  A  test  shaft  1 1 70  feet  deep  was  sunk  near  Atchison,  Kansas, 
but  it  has  not  been  regularly  operated.  With  the  exception  of  this 
one  the  deepest  shaft  is  about  800  feet  and  is  found  in  the  McAlester 
district  of  Oklahoma.  In  Arkansas  the  deepest  shaft  is  about  500 
feet  and  in  Texas  the  shafts  are  comparatively  shallow. 

In  the  northern  Great  Plains  province  mining  has  not  been  carried 
beyond  about  500  feet.  A  shaft  480  feet  deep  has  been  reported 
from  the  Judith  Basin  region  and  there  are  some  less  than  400  feet 
near  Sheridan,  in  the  Fort  Union  region.  In  the  Black  Hills  region 
the  maximum  depth  is  not  over  400  feet  and  in  the  Assinniboine 
region  of  northern  Montana  not  over  300  feet. 

In  the  Rocky  Mountain  province,  owing  to  more  intense  folding 
and  faulting,  the  depth  of  the  mines  is  considerably  greater  than  in 
the  Great  Plains  or  the  Interior  province.  In  Wyoming,  at  Rock 
Springs,  there  is  a  shaft  about  2000  feet  deep  and  in  the  Hams  Fork 
region  there  is  one  which  is  reported  to  be  over  1600  feet.  At  Coke- 
dale,  Montana,  a  mine  was  worked  at  a  depth  of  1300  feet  and  near 
Carbondale,  Colorado,  the  Spring  Gulch  mine  is  down  about  1500 


THE  MINIMUM  THICKNESS  OF  COAL  SEAMS  MINED  253 

feet.  In  southern  Colorado  and  northern  New  Mexico  there  are  some 
mines  working  at  a  depth  of  over  noo  feet,  and  in  the  vicinity  of 
Glenwood  Springs,  and  at  Canon  City,  Colorado,  shafts  are  about 
1000  feet  deep.  Elsewhere  in  the  Rocky  Mountain  province  the 
mines  are  generally  less  than  600  feet  deep.  In  the  Pacific  Coast 
province  the  deepest  mines  are  found  in  Washington.  The  Roslyn 
mine  is  said  to  be  over  700  feet  deep.  In  the  Coos  Bay  field  of  Oregon 
the  coals  lie  under  500  feet  of  strata  and  in  central  California  the  depth 
is  about  300  feet. 

The  maximum  depth  of  coal  mines  in  foreign  countries.  —  The 
deepest  shaft  in  the  world  is  in  Belgium  and  the  latest  figures  avail- 
able give  its  depth  as  3937  feet.  Other  mines  in  the  Mons  district 
of  that  country  run  from  2500  to  over  3000  feet.  The  average  through- 
out Belgium  is  placed  at  1444  feet  by  E.  Loze. 

In  England  the  Rams  mine  at  Manchester  is  not  far  short  of  the 
depth  of  the  Belgian  shaft,  being  over  3480  feet;  a  seam  2  to  6  feet 
in  thickness  is  worked  at  this  mine.  In  the  same  district  there  are 
two  other  mines  each  over  3300  feet  in  depth,  but  these  are  not  classed 
as  shafts.  A  number  of  mines  in  other  fields  run  from  2000  feet  to 
over  3000  feet.  In  South  Wales  the  Ocean  Collieries  reach  2700  feet.1 
In  Scotland  the  deepest  workings  are  near  Edinburgh  and  they  are 
down  to  2700  feet.  The  deepest  shaft  in  Great  Britain  is  said  to  be 
2820  feet,  but  some  of  the  collieries  mentioned  above  are  considerably 
deeper  than  this  shaft.  In  France  some  mines  reach  3000  feet  and 
in  Germany  mining  has  been  carried  to  over  3100  feet.  In  the  Rhen- 
ish-Westphalian  district  the  average  depth  of  the  mines  is  said  to  be 
about  1 700  feet. 

Australia  has  a  shaft  2937  feet  deep  near  Sydney  Harbor,  New 
South  Wales.  This  shaft  was  sunk  to  a  3-foot  bed  of  coal  which  out- 
crops at  Newcastle  and  dips  southward  towards  Sydney. 

THE  MINIMUM  THICKNESS  OF  COAL  SEAMS  MINED 

There  are  several  factors  which  govern  the  minimum  thickness  at 
which  coal  seams  may  be  worked.  The  most  important  of  these 
factors  are:  the  market  for,  and  the  character  of,  the  coal;  the 
nature  of  the  enclosing  rocks;  the  association  of  a  thin  seam  with 
other  seams;  the  depth  of  the  seam;  and  the  training  of  the  miners. 
1  Report  of  the  Royal  Commission  on  Coal  Supplies,  1871  and  1901-1905. 


254 


PROSPECTING  AND   VALUATION  OF  COAL  LANDS 


So  far,  much  thinner  beds  are  worked  in  some  foreign  countries  than 
in  the  United  States.  The  cost  of  mining  thin  seams  usually  increases 
rapidly  as  most  miners  demand  a  bonus  or  refuse  to  work  the  seam  if 
it  be  less  than  a  certain  thickness.  A  mine  manager  in  New  Zealand 
stated  that  the  labor  conditions  there  prohibit  the  working  of  any 
seam  less  than  4  feet  thick  and  the  contract  price  for  mining  at  one 
mine  visited  by  the  writer  was  2  shillings  8  pence  for  a  seam  4  feet 
to  4  feet  6  inches  thick  down  to  2  shillings  4  pence  for  a  seam  5  feet 
thick  or  over,  showing  a  decrease  in  cost  of  mining  of  4  pence  per  ton 
for  an  increase  in  thickness  of  6  inches  or  more. 

Thin  seams  mined  in  the  United  States.  —  Owing  to  the  high 
quality  of  certain  thin  seams  of  coal  or  their  chance  location  near  a 
large  city  or  important  industrial  center,  the  working  of  them  is  not 
confined  to  any  particular  part  of  the  country.  The  following  table 
compiled  from  the  work  by  Fisher1  shows  the  thickness  of  the  thinnest 
seams  reported  as  worked  in  the  various  states. 

TABLE  SHOWING  THE  THICKNESS  OF  THIN  COAL  SEAMS 
WORKED   IN  VARIOUS   STATES 


State 

Thickness  of  Seam 

Alabama 

22-24  inches. 
14  inches.               From  a  stripping. 

18-42  inches.         From  a  drift. 
18-84  inches.         From  a  drift. 
20  inches.               From  a  slope. 
17  inches.               From  a  drift. 
22  inches. 
14-18  inches.         From  a  shaft  230  feet. 
15-18  inches.         From  a  shaft. 
24  inches. 
30  inches. 
24  inches. 
12  inches.              From  a  shaft  44  feet. 
12  inches.              From  a  drift. 
30  inches  . 
7-15  inches. 
26  inches. 
22  inches. 

1  8  inches. 
17-48  inches. 
22  inches. 
19  inches.              From  a  shaft. 
20-24  and  24-36  inches. 
16  inches. 

Arkansas    

Colorado 
Anthracite  

Bituminous  

Illinois  

Illinois  

Indiana 

Iowa 

Kansas 

Kentucky 

Maryland 

Michigan  

Missouri  

Missouri  

Montana  

New  Mexico  

Ohio  

Oklahoma 

Pennsylvania 
Anthracite  field 

Western  Clearfi  eld  district  .  . 
Tennessee  

Texas     

West  Virginia  

Wyoming   .  . 

Op.  cit.,  p.  69. 


VALUE  OF  COAL  LAND  PER  FOOT- ACRE          255 

Many  of  the  thin  seams  in  this  table  are  mined  for  local  use  and 
nearly  all  of  them  are  comparatively  shallow.  Some  are  from  drifts 
and  some  from  strippings,  so  that  on  the  whole  their  thickness  is 
rather  below  a  good  minimum  for  ordinary  mining  operations, 
although  the  official  regulations  governing  coal  lands  of  the  United 
States  place  the  minimum  limit  of  thickness  for  a  workable  seam  at 
14  inches. 

Thin  seams  mined  in  other  countries.  —  Some  very  thin  seams  of 
coal  of  special  quality  have  been  worked  in  foreign  countries.  A 
bed  of  cannel  8  inches  thick  has  been  mined  in  Lancashire,  England, 
and  this  probably  represents  the  thinnest  seam  on  record.  Many 
beds  ranging  from  10  inches  to  20  inches  and  consisting  of  various 
types  of  bituminous  coal  have  been  mined  in  different  parts  of  England 
and  Wales,  while  in  Scotland  beds  ranging  from  15  inches  upward 
in  thickness  have  been  worked. 

In  Belgium  several  seams  not  more  than  n  inches  thick  have  been 
worked,  and  other  seams  13-15  inches  thick  are  regularly  mined  where 
the  coal  is  of  high  grade. 

ESTIMATION  OF  THE  VALUE  OF  COAL  LAND  PER  FOOT-ACRE 

The  price  of  coal  at  the  mine  and  the  cost  of  mining.  —  The  value 
of  an  acre  of  coal  land  in  the  United  States  before  the  war  varied  all 
the  way  from  $10  to  $2000.  The  latter  figure  is  that  stated  by 
Ashley1  for  some  of  the  land  in  the  Connellsville  district  of  Pennsyl- 
vania. There  are,  however,  some  areas  which  are  held  at  a  much 
higher  figure  than  this. 

In  attempting  to  arrive  at  the  value  of  the  coal  in  the  ground  the 
price  per  ton  at  the  mine  and  the  possible  fluctuations  in  price  are 
taken  as  a  basis.  The  figures  given  below  represent  the  price  of 
coal  at  the  mine  in  various  states  for  the  years  1912,  1913,  and  1914? 
and  they  may  be  taken  as  an  indication  of  the  prevailing  prices  in 
different  parts  of  the  country  although  it  must  be  remembered  that 
the  price  varies  with  the  demand,  and  the  location  will  have  a  great 
influence  upon  the  local  price.  For  example,  small  outputs  of  coal 
have  sold  as  high  as  $4.10  per  ton  at  the  mine  in  Idaho  even  in  normal 

1  Ashley,  G.  H.,  The  valuation  of  public  coal  lands.    U.  S.  Geol.  Survey,  Bull.  424, 
1910. 

2  Mineral  Resources,  U.  S.  Geol.  Survey,  1914. 


256 


PROSPECTING   AND  VALUATION  OF   COAL  LANDS 


years,  and  recently  during  a  period  of  scarcity  reports  have  been  re- 
ceived of  coal  selling  for  $10.00  and  $11.00  a  ton  at  some  mines  in 
Pennsylvania. 

TABLE  SHOWING  THE  AVERAGE  PRICE 
PER  SHORT  TON  AT  THE  MINE 


State 


1912 


1913 


1914 


Alabama $  .29 

Arkansas .71 

California a  .33 

Colorado .49 

Georgia .49 

Illinois .17 

Indiana .14 

Iowa .80 

Kansas .62 

Kentucky .02 

Maryland .18 

Michigan .99 

Missouri .76 

Montana .82 

New  Mexico .42 

North  Dakota .53 

Ohio .07 

Oklahoma .14 

Oregon .60 

Pennsylvania  —  Bituminous .05 

Anthracite .11 

South  Dakota 

Tennessee .14 

Texas  .67 

Utah .67 

Virginia o .  96 

Washington 2 .39 

West  Virginia o .  94 

Wyoming i .  58 

Average  Bituminous 1.15 

Average  Anthracite  of  Pennsylvania 2.11 


$1.31 
1.76 

«3-54 
•52 


•14 
.11 

•79 
•67 
•OS 
-24 
•99 
•73 
•74 
.46 
•52 
.10 
•05 
•53 
.11 

•13 
.96 
•14 
•77 
•65 
.01 
•38 
.01 
•56 
.18 
2.13 


1.72 
62.85 
.66 
•44 

.12 
.IO 

•79 
.64 
.02 
.27 
•99 
•73 
•75 
.61 

•52 


06 

2.78 

1.07 

2.07 

•93 

•14 

.69 

•59 
.01 

2.20 
0-99 

i-55 
1.17 
2.07 


a  Includes  Alaska. 

b  Includes  Idaho  and  Nevada. 

After  a  consideration  of  many  fields  Findlay1  concludes  that  the 
cost  of  mining  bituminous  coal,  including  operating  and  related  ex- 
penses amounts  on  the  average  to  about  96  per  cent  of  the  sale  price. 
The  average  cost  per  short  ton  to  the  Pittsburgh  Coal  Company  from 
a  large  number  of  mines  for  five  years  was  89  cents  and  to  the  Mononga- 
hela  River  Consolidated  Coal  and  Coke  Company  for  nine  years, 
91  cents. 

1  J.  R.  Findlay,  The  cost  of  mining,  Eng.  and  Min.  Jour.,  Vol.  87,  p.  948,  1909. 


VALUE  OF  COAL  LAND  PER  FOOT-ACRE 


257 


In  Pennsylvania,  the  cost  of  mining  anthracite  is  considerably 
higher  than  that  of  mining  bituminous  coal.  The  following  figures 
show  the  cost  per  long  ton  to  three  large  companies  in  1905.* 

The  Delaware,  Lacka wanna  and  Western $i .  80 

The  Delaware  and  Hudson 2 . 09 

The  Lehigh  Coal  and  Navigation  Company 2 . 02 

Between  the  years  1902  and  1908  the  costs  to  the  Philadelphia  and 
Reading  Coal  and  Iron  Company  varied  from  $i  .85  to  $2 .00  per  short  ton. 

The  reports  published  by  the  committee  of  the  Federal  Trade 
Commission2  show  the  following  figures  for  the  cost  of  producing  coal 
in  the  several  states  mentioned,  during  recent  years. 
PENNSYLVANIA  ANTHRACITE;    AVERAGE  COST  PER  GROSS  TON 


Labor 

Supplies 

General 
Expenses 

Total  Cost 
f.o.b.  mine 

1913-1918,  inclusive 

$1.58-3.31 

$0.29-0.80 

$0.33-0.61 

$2.59-5.11 

AVERAGE  COST  PER  NET  TON  OF  BITUMINOUS  COAL. 


Labor 

Supplies 

Total  cost  f.o.b.  mine 

Margin  realized 

Pennsylvania 
1916        $0.82 
1917-18  $0.88-1.38 

1916        $0.92 
1917-18  $1.12-1.73 
Illinois,  5  districts. 
1916        $0.74-1.48 
i  917-1  8  $0.83-2.26 
Ohio,  8  districts. 
1916        $o  78—1  19 

S.  W.  field. 

$0.12 

$0.17-0.27 
Central  field 

$0.10 

$0.15-0.31 

$0.05-0.16 
$0.07-0.32 

$1.19 
$1.35-$!.  94 

$1.32 
$1.62-2.38 

$0.94-1.84 
$1.05-2.85 

$1    OO—  I    4.4 

$0.17 
$0.55-1.40 

$0.08 
$0.64-1.10 

$0.03-0.12 

$O  .  2O-O  .  80 

IQI7            $O   Q8—  I    6^ 

$1    1<\—  2    21 

)- 

1918           $1    25—2    24 

$1    73—2    Q6 

$0.54-1.03 

Indiana,  2  districts. 
1916        $o.  87—1  .52 

$1  .  OQ—  I  .  QQ 

1917        $1.08—1.73 

$i  .37—2  .  16 

1  .„, 

1918        $i  .42—2  .  25 

$i  .  8^—2  .  77 

}  $0.45-0.  51 

Michigan. 
1916        $1.58 

$2.08 

1917        $1.95 

$2  -55 

1  *,      .. 

1918           $2    52 

$3  38 

}$o.65 

Alabama,  3  districts. 
1918        $i  53—2  oo 

$2    17-2    ^8 

Tennessee,  3  districts. 
1918        $i  .30—2  .  14 

Si  .77—2  84 

Kentucky,  4  districts. 
1918        $1.25-1.61 

$1  .  74-2  .  28 

1  Chance,  H.  M.,  The  cost  of  mining  coal,  Eng.  and  Min.  Jour.,  Vol.  87,  p.  1099,  1909. 

2  Reports  of  the  Federal  Trade  Commission  on  Coal,  June  30,  1919. 


258  PROSPECTING  AND   VALUATION  OF   COAL   LANDS 

The  general  expense  increased  gradually  during  the  six  years,  but 
the  lowest  labor  cost  as  well  as  the  lowest  total  cost  was  in  the  period 
April  to  August,  1915. 

The  margin  realized  on  the  mining  operations  from  1913-1918 
was  as  follows :  1913,10.31-0.44;  1914,10.22-0.50;  1915,  $0.90-0.50; 
1916,  $0.38-0.57;  1917,  $0.54-0.72;  1918,  $0.35-0.39. 

Weight  of  coal  in  a  foot-acre.  —  The  amount  of  coal  under  a  given 
area  is  estimated  by  the  foot-acre  and  it  is  directly  related  to  the 
specific  gravity  of  a  solid  mass  of  the  coal.  A  cubic  foot  of  water 
weighs  62.5  pounds.  A  cubic  foot  of  coal  with  a  specific  gravity  of  1.3, 
a  good  average  for  bituminous  coal,  will,  therefore,  weigh  81.25  pounds. 
This  gives  24.6  cubic  feet  per  short  ton  and  27.5  cubic  feet  for  a  long 
ton  of  2240  pounds.  It  is  often  assumed  that  0.9  cubic  yard  of 
bituminous  coal  equals  one  ton.  This  is  equivalent  to  24.3  cubic 
feet  per  short  ton  and  corresponds  very  well  with  the  figure  given 
above.  Good  Pennsylvania  anthracite  will  weigh  in  the  block  about 
92  pounds  and  in  lump  57  pounds  to  the  cubic  foot. 

An  acre  contains  43,560  square  feet  and  a  foot-acre  that  number 
of  cubic  feet.  This  would  yield  about  1770  short  tons  providing  it 
could  all  be  extracted  in  mining.  The  percentage  recoverable  in 
mining  will  vary  greatly  according  to  conditions,  such  as  the  thickness 
of  the  seam,  its  freedom  from  partings  and  irregularities,  the  condition 
of  the  roof  and  other  things,  such  for  example  as  location  beneath  a 
town  or  city.  Some  companies  under  favorable  conditions  recover 
97  to  98  per  cent  of  the  coal  while  others  do  not  take  out  more  than 
50  per  cent  or  about  880  tons  per  foot-acre.  A  fair  average  might  be 
80  per  cent  recovered,  which  gives  about  1400  tons  per  foot-acre. 
A  5-foot  seam  would  therefore  yield  on  this  basis  about  7000  tons 
per  acre.  It  should  be  borne  in  mind  that  it  may  be  impossible  to 
mine,  by  present  methods,  more  than  a  small  portion  of  a  bed  which  is 
more  than  30  feet  thick,  and  an  allowance  must  be  made  for  this 
difficulty. 

Estimate  of  coal  in  seams  of  varying  thickness.  —  It  almost  in- 
variably happens  that  when  a  geologist  examines  a  coal  property  he 
must  estimate  the  coal  in  a  number  of  seams  of  varying  thickness 
lying  one  above  another.  The  best  procedure  is  first  to  secure  a  map 
of  the  property  outlined  on  cross-section  paper,  and  then  proceed  to 
divide  the  property  into  areas  beneath  each  of  which  the  average 


ROYALTIES  PAID  ON  LEASES  259 

thickness  of  the  coal  is  estimated,  from  all  the  available  data,  to  be  a 
certain  figure.  The  whole  property  is  divided  up  in  this  way,  and  the 
sum  of  the  tonnages  computed  for  the  various  areas  will  give  the 
total  tonnage  for  the  property.  The  larger  the  number  of  areas  into 
which  the  property  is  divided,  the  greater  the  probability  of  securing 
an  accurate  estimate,  in  most  cases.  The  seams  may  be  lettered  or 
numbered  and  then  treated  separately  in  dividing  the  property  into 
the  various  areas. 

Royalties  paid  on  leases.  —  The  royalty  paid  on  coal  -lands  varies 
greatly  in  different  fields.  The  variation  is  very  much  greater  than 
in  the  price  of  coal  at  the  mine  in  the  different  fields,  and  the  differ- 
ence in  royalty  demanded  does  not  always  correspond  to  the  differ- 
ence in  the  price  per  acre,  which  might  be  demanded  for  land  in 
different  areas.  This  is  because  the  rate  at  which  the  coal  is  mined 
has  an  important  bearing  on  the  relative  income  from  the  royalty  and 
that  from  the  sale  of  the  land,  since  the  interest  on  the  money  and  the 
taxes  amount  to  a  considerable  item  if  the  time  required  for  mining  the 
coal  be  long.  According  to  Ashley1  the  royalties  paid  in  the  Anthracite 
region  of  Pennsylvania  previous  to  1910  ran  up  to  50  cents  or  locally 
to  $1.00  a  ton,  and  the  writer  has  obtained  similar  figures  for  this 
field  in  more  recent  years,  with  some  running  as  high  as  $1.40  a  ton. 
In  the  bituminous  fields  of  the  state  the  royalties  varied  from  5  to 
30  cents  except  in  a  few  cases  in  which  they  went  up  to  $1.00  or  more 
in  the  Connellsville  field.  The  average  for  the  state  was  perhaps  10 
cents  a  ton.  In  Ohio  the  royalty  varied  from  8  cents  to  15  cents. 
In  Illinois  2  cents  to  25  cents  has  been  paid,  and  in  Indiana  2  cents  to 
10  cents.  The  West  Virginia  royalties  which  have  been  reported  run 
from  8  to  24  cents,  the  latter  in  the  coke  regions.  In  Kentucky, 
Tennessee  and  Alabama  the  figures  are  from  3  cents  to  12  J  cents  and 
in  Arkansas  and  Oklahoma  3  to  8  cents.  In  Colorado,  state  lands 
pay  10  cents  and  other  lands  from  8  to  27  cents.  On  account  of  the 
great  local  demand  for  coal  in  limited  areas  in  Wyoming  some  roy- 
alties have  been  reported  as  high  as  $1.00  a  ton,  but  they  usually  run 
from  3  to  10  cents.  Montana  royalties  are  about  15  cents  so  far  as 
known,  and  in  Utah  some  local  mines  have  paid  as  high  as  75  cents. 
All  these  figures  have  changed  rapidly  during  the  last  few  years  of 
inflated  prices. 

1  Op.  cit.,  pp.  9  and  10. 


260  PROSPECTING  AND   VALUATION  OF   COAL  LANDS 

In  many  of  the  fields  where  the  royalties  mentioned  above  are  paid 
there  is  also  a  bonus  and  in  most  cases  a  minimum  yearly  royalty  is 
demanded  in  the  contract.  In  some  states  the  royalty  decreases  as 
the  output  increases  and  in  Kentucky  it  fluctuates  with  the  thickness 
of  the  seam. 

CLASSIFICATION  AND  VALUATION  OF  COAL  LANDS  BY  THE 
UNITED  STATES  GOVERNMENT 

The  "  Regulations  on  the  Classification  and  Valuation  of  Coal 
Lands,"  adopted  by  the  Secretary  of  the  Interior  on  April  10,  1909, 
contain  the  following  clauses: 

I.  For  purposes  of  classification  and  valuation,  coal  deposits  shall 

be  divided  into  four  classes. 

A,  Anthracite,  semianthracite,  coking  and  blacksmi thing  coals. 

B,  High-grade  bituminous,  non-coking  coals  having  a  fuel  value 

of  not  less  than  12,000  B.t.u.  on  an  unweathered,  air-dried 
sample. 

C,  Bituminous  coals  having  a  fuel  value  of  less  than  12,000  B.t.u. 

on  an  unweathered,  air-dried  sample,  and  high-grade  sub- 
bituminous  coals  having  a  fuel  value  of  more  than  9500 
B.t.u.  on  an  unweathered,  air-dried  sample. 
Z),  Low-grade  subbituminous  coals  having  a  fuel  value  below 
9500  B.t.u.  on  an  unweathered,  air-dried  sample,  and  all 
lignite  coals. 

II.  Lands  underlain  by  coal  beds,  none  of  which  contain  14  inches 
or  over  of  coal,  exclusive  of  partings,  of  Class  A,  B,  or  C,  or 
over  36  inches  of  Class  D,  shall  be  classified  as  non-coal  land. 

III.  Lands  containing  coals  of  classes  A  and  B  of  any  thickness 
at  depths  greater  than  3000  feet  shall  be  classified  as  non-coal 
lands,  except  where  the  rocks  are  practically  horizontal  and 
the  coal  lies  within  2  miles  of  the  outcrop  or  point  at  which  it 
can  be  reached  by  a  30oo-foot  shaft. 

IV.  Lands  containing  coals  of  class  C  of  any  thickness  at  a  depth 
greater  than  2000  feet  shall  be  classed  as  non-coal  lands,  ex- 
cept where  the  rocks  are  practically  horizontal  and  the  coal 
lies  within  2  miles  of  the  outcrop  or  point  at  which  it  can  be 
reached  by  a  2000-foot  shaft. 


CLASSIFICATION  AND   VALUATION  OF    COAL  LANDS  261 

V.  Lands  containing  coals  of  Class  D  of  any  thickness  at  a  depth 

greater  than  500  feet  shall  be  classed  as  non-coal  lands,  except 
where  the  rocks  are  practically  horizontal  and  the  coal  lies 
within  i  mile  of  the  outcrop  or  point  at  which  it  can  be  reached 
by  a  500  foot  shaft. 

VI.  The  prices  of  coal  lands  of  Classes  A,  B,  and  C  shall  be  de- 
termined on  the  basis  of  estimated  tonnage  at  the  rate  of  one- 
half  cent  to  i  cent  per  estimated  ton  for  Class  C,  i  to  2  cents 
per  estimated  ton  for  Class  B,  2  to  3  cents  per  estimated  ton 
for  Class  A,  when  the  lands  are  within  15  miles  of  a  completed 
railroad  and  half  that  much  when  at  a  greater  distance;   but 
the  price  shall  in  no  case  exceed  $300  per  acre,  except  in  dis- 
tricts which  contain  large  coal  mines  where  the  character  and 
extent  of  the  coal  are  well  known  to  the  purchaser.     When, 
however,  topographic  conditions  affect  the  accessibility  of  the 
coal  the  land  within  the  1 5-mile  limit  may  be  given  a  lower 
valuation,  but  in  no  case  shall  it  be  placed  at  less  than  the 
minimum,  and  a  graded  allowance  may  be  made  for  increasing 
depth,  with  the  same  restriction. 

VII.  The  rates  per  ton  in  the  preceding  paragraph  are  based  on 
the  assumption  that  only  one  bed  is  present.     If  more  than  one 
bed  occurs  in  any  tract  of  land  in  such  relationship  that  the 
mining  of  one  will  not  necessarily  disturb  the  other,  then  for 
the  second  bed  there  shall  be  added  to  the  price  of  the  first 
bed  60  per  cent  of  the  value  of  the  second  bed  according  to  the 
schedule,  40  per  cent  of  the  value  of  the  third  bed,  and  30  per 
cent  of  the  value  of  each  additional  bed;   but  the  estimated 
price  for  coal  shall  in  no  case  exceed  $300  per  acre,  except  in 
districts  which  contain  large  coal  mines  where  the  character 
and  extent  of  the  coal  deposits  are  well  known  to  the  purchaser. 
Where  a  bed  is  over  15  feet  thick,  the  normal  value  shall  be 
placed  only  on  15  feet;   the  next  15  feet  or  part  thereof  shall 
be  valued  at  60  per  cent  of  the  normal;    the  next  15  feet  or 
part  thereof  at  40  per  cent  of  the  normal  and  the  rest  of  the 
bed  at  30  per  cent  of  the  normal. 

VIII.  The  tonnage  shall  be  estimated  for  the  purpose  of  valuation 
on  the  basis  of  1000  tons  recovery  per  acre-foot. 


262  PROSPECTING  AND   VALUATION  OF   COAL  LANDS 

IX.  The  price  of  lands  of  Class  D  shall  be  the  minimum  provided 
by  law,  $20  per  acre  when  within  15  miles  of  a  railroad  and 
$10  per  acre  when  at  a  greater  distance. 

X.  In  all  valuations  of  coal  lands  any  special  conditions  enhanc- 
ing the  value  of  the  land  for  coal-mining  purposes  shall  be 
taken  into  consideration. 

XI.  When  only  a  part  of  a  smallest  legal  subdivision  is  underlain 
by  coal  the  price  per  acre  shall  be  fixed  by  dividing  the  total 
estimated  coal  values  by  the  number  of  acres  in  the  sub- 
division, but  in  no  case  shall  this  be  less  than  the  minimum 
provided  by  law. 

XII.  When  lands  which  were  at  the  time  of  classification  more 
than  15  miles  from  a  railroad  are  brought  within  the  1 5-mile 
limit  by  the  beginning  of  operation  of  a  new  road  all  values 
given  in  the  original  classification  shall  be  doubled  by  the 
register  and  receiver. 

XIII.  Except  in  case  of  entries  now  pending  or  entries  made  prior 
to  classification,  review  of  classification  or  valuation  may  be 
had  only  upon  application  therefor  to  the  Secretary  accompa- 
nied by  a  showing  clearly  and  specifically  setting  forth  condi- 
tions not  existing  or  known  at  time  of  examination.1 

In  formulating  these  regulations  it  was  desired  that  the  price  should 
be  such  that  it  would  discourage  private  citizens  from  buying  coal 
lands  for  speculation  with  a  view  to  holding  them  for  future  favorable 
conditions,  but  at  the  same  time  that  it  should  not  retard  the  business 
of  legitimate  coal  mining.  The  royalty  rate  taken  as  a  rough  standard 
in  figuring  the  price  per  ton  was  10  cents,  since  it  was  believed  to  be 
a  fair  average  for  the  whole  country.  On  the  adoption  of  the  above 
regulations  much  land  was  withdrawn  from  entry  in  order  that  it 
should  be  classified  and  valued  by  the  Geological  Survey.  The  amount 
of  land  withdrawn  from  coal  entry  on  November  i  of  that  year  in  the 
nine  states,  Wyoming,  Washington,  Utah,  Oregon,  Montana,  New 
Mexico,  Colorado,  South  Dakota,  and  North  Dakota,  amounted  to 
31,872,171  acres.  The  area  withdrawn  from  all  entry  in  the  same 
states  on  that  date  was  11,862,576  acres,  and  the  amount  of  classi- 
fied land  restored  to  entry  was  35,915,255  acres. 

1  Ashley,  Op.  cit.,  pp.  37  and  42. 


CLASSIFICATION  AND   VALUATION  OF   COAL   LANDS  263 

There  has  been  a  growing  feeling  among  government  officials  and 
others  interested  in  coal  lands  that  the  public  coal  lands  should  be 
leased  for  the  purpose  of  mining  only  and  the  title  to  the  land  should 
rest  with  the  State.1  Colorado  has  had  for  many  years  a  leasing 
system  on  a  royalty  basis  of  10  cents  a  short  ton  run-of-mine,  less  one- 
twelfth  of  the  minimum  annual  royalty  which  shall  have  been  paid 
at  the  beginning  of  the  year.  This  minimum  royalty  is  paid  whether 
any  coal  is  mined  or  not.  Wyoming  also  adopted  the  leasing  system 
in  1907  and  in  that  state  an  "  advance  royalty  "  is  paid  and  is  applied 
on  a  royalty  of  6  cents  on  all  coal  mined,  and  sold  up  to  25,000  tons, 
5  cents  if  amount  is  between  25,000  and  50,000  tons,  4  cents  if  it  falls 
between  50,000  and  100,000,  and  3  cents  if  it  exceeds  100,000  tons  per 
annum.  The  lessee  must  spend  not  less  than  $200  on  development 
work.  As  indicated  above,  Congress  has  also  recently  passed  a  leas- 
ing bill  which  permits  the  leasing  of  public  coal  lands  from  the 
Government. 

1  Bain,  H.  F.,  Leasing  the  Federal  Coal  Lands,  Min.  and  Sci.  Press,  Vol.  96,  p.  73, 1908. 
The  value  of  Coal  Land.  Mines  and  Minerals,  Vol.  29,  p.  366. 


CHAPTER  X 

MINING   OF  COAL 

Introduction 

The  process  or  mining  coal  has  become  a  highly  developed  art  and 
a  detailed  description  of  all  methods  employed  would  embrace  a  very 
extensive  literature.  In  this  chapter  only  the  main  methods  employed 
are  described  and  reference  is  made  to  a  few  of  the  larger  works  in 
which  the  details  of  the  various  operations  are  found.1  With  the 
introduction  of  labor-saving  machinery,  resulting  especially  from  the 
more  extensive  use  of  electricity  in  mines,  rapid  changes  in  methods 
are  taking  place  and  before  long  the  bulk  of  all  coal  mined  under  favor- 
able conditions,  in  the  more  advanced  countries  will  be  cut,  broken 
and  loaded  by  machinery.  The  development  of  large  steam  shovels 
has  made  it  possible  to  strip  many  coal  seams  formerly  out  of  reach 
in  open  pit  mining  and  to  mine  them  on  the  surface,  while  the 
working  out  of  the  thicker  seams  underground  necessitates  the  mining 
of  thinner  seams.  In  this  work  the  use  of  mechanical  conveyors 
and  other  labor-saving  devices  is  becoming  more  common. 

Mining  Methods 

The  main  methods  employed  in  coal  mining  may  be  classed  as  (i) 
Open  work  and  (2)  Underground,  or  dosed  work.  The  first  is  fre- 
quently known  as  stripping  or  open-pit  mining.  The  underground 
methods  may  be  divided  into  Room-and-pillar  and  Longwall  methods, 
and  there  are  several  modifications  of  each  of  these. 

STRIPPING  METHOD 

In  areas  where  a  good  seam  of  coal  underlies  a  thin  overburden 
it  pays  to  strip  off  the  covering.  The  depth  to  which  this  stripping 
may  be  profitably  carried  depends  upon  many  factors.  It  has  been 

1  Coal  miner's  pocketbook,  McGraw  Hill,  1916.  Peele's  Handbook  for  mining  en- 
gineers, John  Wiley  &  Sons,  Inc.,  1918.  Practical  coal  mining  by  W.  S.  Boulton,  London, 
1907.  Vols.  1-6.  Colliery  working  and  management,  Bulman  and  Redmayne,  1912. 

264 


STRIPPING  METHOD 


265 


considered  in  the  past  that  a  foot  of  overburden  could  be  removed 
by  hand  for  each  foot  of  coal  obtained.  Most  stripping  is  done  at 
the  present  day,  however,  by  the  large  steam  shovel  of  ordinary  type, 
the  rotary  shovel  or  the  dragline  excavator.  In  Illinois  hydraulic 
means  are  employed  to  some  extent  in  stripping.  The  proportion 
of  overburden  to  coal  which  may  be  profitably  removed  has  therefore 
increased  to  from  3  to  6  times  the  figure  stated.  The  proportion  will 
vary  greatly  according  to  the  grade  and  the  price  of  the  coal  and  the 
nature  of  the  overlying  rock.  A  heavy,  little-jointed  sandstone  or 
limestone  which  requires  blasting,  or  a  loose  rock  which  is  full  of  water 
and  runs  readily  may  increase  to  a  large  degree  the  relative  cost  of 
stripping. 


FIG.  83.  —  Stripping  on  the  Mammoth  Seam  near  Hazleton,  Pa.     (Photo  by  E.  S. 

Moore.) 

In  the  anthracite  region  of  Pennsylvania  extensive  stripping  oper- 
ations are  carried  on,  especially  in  the  district  around  Hazleton  where 
the  Mammoth  seam  is  thick,  (Figs.  76  and  83).  In  some  places  this 
seam  runs  from  50  feet  up  to  100  feet  or  more,  where  it  is  duplicated  by 
folding,  and  an  overburden  up  to  90  feet  in  thickness  has  been  removed, 
while  some  of  the  projected  strippings  will  require  the  removal  of 
nearly  200  feet  of  overburden  as,  for  example  at  Locust  Mountain. 
A  great  deal  of  coal  is  obtained  by  this  method  which  could  not  be 
obtained  by  underground  mining,  especially  in  those  areas  where 


266  MINING  OF  COAL 

the  early  mining  operations  left  much  coal  in  the  ground  and  a 
great  deal  of  it  in  such  condition  that  underground  mining  is  very 
difficult,  dangerous  or  even  impossible. 

In  some  of  the  bituminous  fields  of  the  United  States  open  cuts  are 
extensively  worked,  particularly  in  Alabama,  Missouri,  Kansas,  In- 
diana, Ohio,  Pennsylvania,  Illinois  and  Oklahoma.  In  Missouri  over 
one  million  tons,  or  21.6  per  cent  of  the  coal  mined  in  that  state  in 
1916  was  mined  in  this  way.  Over  12  per  cent  of  the  coal  mined  in 
Indiana  and  a  considerable  amount  of  that  raised  in  Alabama  is  worked 
by  this  method. 

After  the  stripping  is  done  the  coal  is  usually  dug  by  steam  shovels 
of  special  type,  known  as  rotary  shovels,  but  in  a  few  cases  it  is  dug 
by  hand. 

The  main  advantages  of  the  stripping  method  are  in  the  absence 
of  squeezes,  falls  of  roof  and  dangerous  gases  with  accompanying 
explosions.  There  is  no  necessity  for  timbering  or  lighting,  and  the 
work  may  be  more  easily  directed.  Experienced  men  are  not  neces- 
sary except  for  the  management  of  the  steam  shovels,  and  in  case  of 
closing  down  operations  the  damage  by  flooding  of  the  pit  is  not 
usually  so  great  as  the  damage  suffered  by  an  idle  mine.  The  dis- 
advantages are  the  necessity  of  ceasing  work  in  very  stormy  weather 
and  the  collection  in  the  open  pits  of  so  much  water,  and,  in  the  colder 
climates,  of  snow.  It  is  difficult  to  dispose  of  the  overburden  in  some 
regions  and  the  abandoned  pits  are  objectionable,  but  probably  not 
much  more  so  than  a  surface  area  which  is  extensively  caved  after  the 
mining  of  shallow  seams. 

UNDERGROUND  WORKINGS 

MINE  OPENINGS 

In  order  to  reach  the  coal  which  lies  too  deep  for  stripping  oper- 
ations a  tunnel  or  drift  is  driven,  or  a  slope  or  shaft  is  sunk.  A  tunnel 
is  typically  open  at  both  ends  but  the  term  is  often  applied  to  an 
opening  driven  horizontally  or  nearly  so  across  the  measures.  In 
coal  mining,  a  drift  is  usually  regarded  as  an  opening  driven  from  the 
surface  in  the  seam  but  the  term  is  also  used  in  some  cases  where  the 
opening  does  not  reach  the  surface.  A  shaft  is  a  vertical  mine  opening 
driven  from  the  surface.  If  it  is  driven  from  one  seam  to  another  it 


ENTRIES,  HEADINGS,   OR   GANGWAYS  267 

.         i 

is  known  as  a  blind  shaft.     A  slope  is  an  inclined  opening  usually 
driven  on  the  coal  seam  and  used  as  a  haulage  or  other  roadway. 

Shafts.  —  A  shaft  should  be  placed  where  it  will  best  serve  the 
maximum  portion  of  the  area  to  be  mined  and  it  should  be  kept  away 
as  much  as  possible  from  areas  which  are  faulted,  highly  squeezed 
or  subject  to  flooding.  A  shaft  may  be  timbered,  bricked,  concreted 
or  lined  with  metal.  Timber  is  commonly  employed  but  many  of 
the  modern  shafts  in  large  mines  are  concrete  lined  while  brick  is  used 
in  many  mines,  especially  in  Europe.  The  advantage  of  brick  or 
concrete  over  timber  is  in  their  greater  durability,  in  the  absence  of 
danger  from  fire,  and,  in  the  case  of  air  shafts,  in  the  fact  that  they 
offer  much  less  friction  to  the  air  currents  since  the  timbers  tend  to 
create  local  eddies  in  the  current  and  thus  increase  resistance  to 
movement. 

The  shape  of  the  shaft  varies  with  the  conditions.  A  timbered 
shaft  is,  as  a  rule,  rectangular  while  a  brick  or  concrete  shaft  is  usually 
made  circular  or  elliptical.  The  size  depends  chiefly  upon  the  pro- 
posed output  of  the  mine,  the  size  of  the  mine  car  to  be  employed 
and  the  possibility  of  the  formation  of  ice  in  the  compartments  in 
winter.  The  width  of  the  cross  section  may  be  from  5  feet  to  more 
than  double  that  width,  and  the  length  may  exceed  50  feet  where 
there  are  a  large  number  of  compartments  used  in  hoisting  a  big 
output. 

In  most  shafts  there  is  a  compartment  set  apart  for  pipes  and 
ladders  while  the  others  are  used  for  hoisting. 

In  sinking  a  shaft  the  same  methods  are  employed  in  coal  mining 
as  in  metal  mining  and  include  the  blasting  of  the  rock  and  its  re- 
moval by  hoisting  with  windlass  or  steam  hoist.  Where  the  rock 
is  not  firm  or  where  quicksand  or  other  running  ground  is  encoun- 
tered special  methods  such  as  piling,  freezing  or  cementing  must  be 
employed.  A  shield  may  be  used  in  some  cases  to  protect  the  work- 
men from  falling  rock. 

The  laws  of  most  states  require  at  least  two  separate  openings  to 
all  coal  mines  so  that  in  case  of  accident  men  may  have  a  means  of 
escape. 

THE  ROOM-AND  PILLAR-METHOD 

Entries,  headings,  or  gangways.  —  As  the  term  implies  this  method 
consists  in  working  out  rooms,  chambers  or  breasts,  in  the  seam,  leaving 


268 


MINING   OF  COAL 


ENTRIES,   HEADINGS,   OR   GANGWAYS  269 

portions  of  the  coal  between  these  rooms  in  the  form  of  pillars  to  sup- 
port the  roof.  The  portion  of  the  seam  which  is  to  be  mined  from  a 
certain  shaft  or  slope  is  first  split  up  into  a  number  of  sections  by 
driving  passages  from  the  shaft  bottom  or  from  the  slope  as  the  case 
may  be,  (Fig.  84).  These  passages  are  known  as  main  entries  or 
main  headings  in  the  bituminous  mines  and  as  gangways  in  the  an- 
thracite mines  of  America,  and  they  usually  run  to  the  border  of  the 
property.  They  are  as  straight  as  possible  so  as  to  avoid  turns  in 
track  or  sudden  changes  in  direction  of  the  air  currents,  and  where 
used  for  air  courses  the  perimeter  should  be  as  small  as  possible  in 
proportion  to  the  area  so  as  to  reduce  friction  of  air  current  to  a  mini- 
mum. The  nearer  a  square  is  approached  the  less  the  perimeter  for 
the  area  enclosed.  They  are  about  6  feet  high  and  from  6  to  21  feet 
wide,  according  to  the  thickness  of  the  seam,  the  nature  of  the  bottom 
and  roof  of  the  seam,  the  amount  of  output  from  the  mine  and  other 
factors.  If  the  roof  and  bottom  are  bad  it  is  more  difficult  to  carry 
a  wide  entry  and  if  the  seam  is  too  thin  so  that  the  roof  must  be 
brushed  down  by  taking  down  a  lot  of  draw  slate  there  must  be  an 
entry  wide  enough  to  furnish  some  storage  space  for  the  waste  rock. 
It  usually  costs  much  more  to  drive  narrow  entries  than  wide  ones 
in  proportion  to  the  coal  taken  out  as  the  former  operation  is  classed 
as  narrow  work  and  a  higher  charge  is  made  for  all  work  so  classed. 
The  size  of  the  area  mined  from  one  shaft  where  the  seam  is  flat 
will  run  from  several  hundred  to  two  thousand  acres  or  more  depend- 
ing upon  conditions,  and  some  main  entries  are,  therefore,  of  great 
length.  They  are  timbered,  bricked  or  concreted  where  necessary 
to  properly  support  the  sides  and  roof.  Timber  is  more  commonly 
used  but  concrete  is  now  being  extensively  adopted  in  the  larger 
mines  for  at  least  the  part  of  the  entry  near  the  shaft  or  slope. 

In  driving  main  entries  they  are  usually  driven  on  the  dip  of  the 
seam,  if  the  seam  is  inclined,  and  if  it  be  nearly  flat  such  factors  as 
drainage,  direction  of  horsebacks,  direction  of  joints  in  the  coal  or  its 
cleat,  and  direction  of  fractures  in  the  roof  of  the  entries  affect  the 
direction.  From  the  main  entries  cross  entries,  cross  headings,  or 
butts  are  driven,  usually  at  right  angles  to  the  main  passages.  There 
are  some  important  considerations  in  laying  out  the  cross  entries  or 
butt  headings.  They  must  drain  properly  to  the  main  headings  and 
if  possible  any  grade  should  be  used  to  advantage  in  hauling  the  coal. 


270  MINING   OF   COAL 

In  case  a  syncline  or  "  swamp  "  occurs  in  the  mine  the  headings 
should  be  run  so  that  the  rooms  may  be  driven  on  the  rise  from  the 
entry  and  the  coal  thus  worked  down  grade  to  the  main  haulage  lines. 
In  inclined  seams  the  headings  are  driven  so  that  they  follow  closely 
the  strike  of  the  seam,  allowing  for  drainage,  and  each  section  of  the 
mine  in  which  one  or  more  of  these  headings  is  driven  off  the  slope  is 
known  as  a  lift  or  level.  This  term  includes  all  the  workings  lying 
at  approximately  the  same  level  and  connected  with  the  slope  or  shaft 
at  the  same  elevation. 

Entry  systems:  The  number  of  entries  varies  greatly  in  the  mines 
of  different  regions.  There  are  single,  double,  triple,  quadruple,  and 
even  sextuple-entry  systems.  The  first  is  seldom  used  and  is  not 
applicable  to  a  large  mine.  In  it  a  single  entry  is  driven  and  it  serves 
as  the  haulageway  and  intake  air  course.  It  is  inefficient  because  an 
accident  in  the  entry  may  cut  off  the  circulation  of  air,  the  haulage, 
and  the  escape  of  men  from  the  mine. 

The  double-entry  system  is  very  commonly  used  in  America  and  as 
indicated  by  the  name  the  main  and  cross  entries  are  all  driven  in 
pairs.  This  increases  the  efficiency  of  the  mine  as  a  double  track 
increases  that  of  a  railroad.  If  one  entry  becomes  blocked  the  air 
current  and  the  haulage  may  be  shifted  to  the  other,  (Fig.  84  and 
Plate  IX). 

The  triple-entry  system  is  also  frequently  used  and  it  has  an  ad- 
vantage in  that  the  central  passage  may  be  used  as  the  main  haulage 
route  and  at  the  same  time  the  intake  air  course.  The  other  two 
entries  are  the  return  air  courses  for  their  respective  sides  of  the  mine. 

In  the  four-entry  system  there  are  four  entries  driven  side  by  side; 
this  system  is  frequently  adopted,  especially  for  gaseous  mines  and 
those  with  a  large  output  (Fig.  84).  For  those  mines  where  endless 
rope  haulage  is  used  it  has  an  advantage  as  one  entry  may  serve  as  a 
haulage  road  for  loaded  cars  and  the  other  for  empties,  while  the 
other  two  are  the  return  air  courses.  Several  different  arrangements 
are  possible  as  one  entry  may  be  used  for  a  manway  and  intake  air 
course,  one  as  a  haulage  road  and  intake  and  the  other  two  as  return 
air  courses,  or  they  may  be  divided  so  that  the  four  entries  are  oper- 
ated as  pairs. 

In  all  these  systems  where  two  or  more  entries  are  used  the  entries 
are  connected  by  cut-throughs ,  break-throughs  or  cross  cuts,  which 


ROOMS,   CHAMBERS,   OR  BREASTS  271 

are  openings  about  the  same  width  as  the  entries  and  driven  at  right 
angles  to  the  entries,  through  the  pillars  separating  them.  When 
one  of  these  openings  is  driven  at  an  inclination  less  than  90°  to  the 
entry  it  is  known  in  some  localities  as  a  shoofly,  (Fig.  84).  The 
distance  between  these  openings  varies  with  the  law  requirements  of 
the  region,  the  gaseous  nature  of  the  mine  and  other  local  conditions. 
In  the  entries,  spaces  must  be  provided  for  the  temporary  storage  of 
cars  where  they  are  collected  from  the  working  places  and  made  up 
into  trips.  These  track  areas  are  known  as  sidings,  partings  or  lyes, 
and  where  single  track  is  used  for  haulage  the  siding  where  the  cars 
turn  out  to  pass  is  known  as  a  turn-out  or  pass-by. 

Rooms,  chambers,  or  breasts.  —  The  rooms,  chambers  or  breasts 
are  openings  in  the  seam  turned  off  the  cross-entries  and  separated 
by  pillars,  (Fig.  84).  These  rooms  are  laid  out  according  to  a  definite 
system  and  at  stated  intervals.  The  end  of  the  room  where  the  coal 


FIG.  85.  —  Rooms  driven  at  inclination  to  the  entry  in  double  entry  mine. 

is  being  mined  is  known  as  the  face  or  working  face  and  the  side  of  the 
room  or  entry  along  a  pillar  is  the  rib.  The  terms  inby  and  outby 
serve  to  indicate  the  direction  in  the  room,  the  former  meaning  toward 
the  face  and  away  from  the  entry  and  the  latter  the  opposite  direction. 
When  a  room  is  begun  an  opening  known  as  the  neck  or  mouth  is 
made  from  the  entry  and  about  the  same  width  as  the  entry.  This 
is  usually  at  right  angles  to  the  entry  in  flat  or  steeply  pitching  seams, 
but  in  gently  inclined  seams  the  rooms  may  be  inclined  less  than  90° 


272  MINING  OF  COAL 

to  the  entry  and  thus  secure  a  more  gradual  rise  for  hauling  cars  to 
the  face,  (Fig.  85).  Where  the  rooms  are  driven  at  such  an  angle 
their  necks  must  be  longer  in  order  to  leave  sufficient  coal  in  pillars 
to  protect  the  entry.  The  direction  of  the  room  may  also  be  influ- 
enced by  the  fractures  in  the  roof  and  by  the  cleat  in  the  coal.  There 
are  several  terms  describing  the  relation  between  the  direction  of 
these  joints  and  the  direction  of  the  room.  When  the  face  is  parallel 
to  the  main,  or  face  cleat,  and  the  rib  at  right  angles  to  it  the  position 
is  known  as  face  on.  The  opposite  to  face  on  is  end  on,  the  position 

in  which  the  face  is  at  right 
angles  to  the  face  cleat  and 
parallel  to  the  butt  cleats. 
Half  on  is  the  term  used  where 
the  face  of  the  room  makes  an 
angle  of  45°  with  the  face  cleats 
and  short  horn  where  it  makes 
an  angle  of  more  than  45°.  In 
driving  long  horn  the  face  of  the 
room  lies  at  an  angle  less  than 
45°  to  the  face  cleats.  These 

FIG.  86.  -  Double  room  and  break-throughs.   vari°US  P°sitions  have  their  ad- 

vantages  under  different  con- 
ditions because  the  coal  breaks  more  readily  and  leaves  more  lump 
if  mined  from  a  certain  direction  with  relation  to  the  cleats.  The  gas 
may  escape  from  the  coal  more  gradually  if  the  face  lies  across  the  di- 
rection of  the  main  joints  rather  than  parallel  to  them. 

When  the  neck  of  a  room  has  been  driven  a  sufficient  distance  from 
the  entry,  varying  from  6  to  25  feet,  the  room  is  widened  out  on  one 
side  of  the  neck  at  an  angle  of  90°  or  less,  usually  less,  (Fig.  84). 
This  side  is  known  as  the  gob  side  because  the  waste  rock  is  usually 
stored  in  it  and  the  track  is  laid  along  the  opposite  side.  The  width 
of  the  room  will  depend  upon  such  factors  as  the  weight  of  overlying 
strata,  the.  character  of  the  roof  and  bottom  and  the  thickness  of  the 
seam.  A  common  width  is  about  20  feet,  but  it  may  run  from  12 
feet  up  to  40  feet  or  more.  The  length  of  the  room  usually  lies  be- 
tween 150  and  300  feet  although  rooms  are  sometimes  as  much  as 
600  feet  in  length.  A  common  length  is  250  feet.  The  presence  of 
gas  will  usually  affect  the  length  of  the  room  to  some  extent  and  tend 


PILLARS  273 

to  shorten  it.  The  rooms  are  connected  by  cut-throughs ,  or  break- 
throughs, to  permit  the  circulation  of  air  and  the  movement  of  the 
workmen,  and  in  some  cases  a  series  of  these  in  line  may  serve  as  a 
haulage  road.  The  more  gaseous  the  mine  the  more  numerous  the 
break-throughs  should  be.  In  many  fields  their  number  is  fixed  by 
law.  In  the  bituminous  region  of  Pennsylvania  they  cannot  be  more 
than  35  yards  nor  less  than  16  yards  apart. 

In  some  mines  double  rooms  are  driven,  leaving  a  pillar  of  coal  be- 
tween the  double  necks,  (Fig.  86).  The  main  advantage  of  the 
double  room  is  in  the  more  extensive  working  face  provided.  If 
there  be  much  waste  rock  it  may  be  gobbed  along  the  center  of  the 
room  leaving  the  tracks  along  the  ribs  on  either  side. 

Pillars.  —  The  several  types  of  pillars  in  a  coal  mine  comprise : 
the  ordinary  pillars  left  between  entries  and  between  rooms  or  breasts; 
chain  pillars;  shaft  or  slope  pillars;  and  barrier  pillars.  A  chain 
pillar  is  a  long  wide  pillar  left  along  an  entry  or  gangway  from  which 
rooms  are  being  driven  to  protect  that  opening,  and  it  may  be  cut 
through  by  a  number  of  break-throughs.  A  shaft  pillar  or  slope 
pillar  is  left  around  a  shaft  or  slope  in  each  coal  seam  through  which 
the  shaft  or  slope  passes,  to  protect  the  shaft  or  slope  and  the  build- 
ings or  other  structures  on  the  surface  from  damage.  A  barrier  pillar 
is  left  along  the  border  of  a  property  to  protect  adjacent  lands  on 
either  side  of  a  property  line  from  caving  and  from  water  or  gas. 
The  term  is  also  applied  to  a  pillar  left  in  a  mine  to  protect  a  certain 
portion  of  the  mine  from  gas  or  water  or  to  separate  for  some  other 
reason  this  portion  from  the  remainder  of  the  mine. 

Size  of  pillars:  The  size  of  any  of  these  pillars  depends  upon  vari- 
ous conditions  and  can  only  be  determined  from  experience  in  the 
region  being  worked.  The  greater  the  inclination,  depth  and  thick- 
ness of  the  seam,  the  greater  the  quantity  of  water  present,  the  weaker 
the  roof  and  bottom,  the  more  friable  the  coal,  the  more  faulted  the 
overlying  strata,  and  the  longer  the  pillars  must  stand,  the  larger 
they  must  be,  other  things  being  equal.  The  approximate  weight 
of  the  overlying  strata  may  be  figured  by  averaging  the  specific  gravity 
of  the  rock  and  computing  the  weight  of  the  column  of  rock  of  the 
proper  size  and  depth,  but  even  then  the  effects  of  arching  or  bridging 
of  the  heavy  beds  in  the  series  will  not  be  taken  into  account.  The 
average  specific  gravity  of  sandstone  may  be  taken  as  2.3  and  that  of 


274 


MINING  OF  COAL 


I 


•S 


PILLARS  275 

shale  as  2.5,  which  makes  a  cubic  foot  of  sandstone  weigh  about  140 
pounds  and  a  cubic  foot  of  shale  approximately  160  pounds. 

The  distance  between  entries  is  usually  made  from  20  to  60  feet. 
Under  certain  conditions  it  is  necessary  to  leave  extra  entry  pillars 
to  protect  the  entry,  and  these  may  be  very  wide,  sometimes  exceed- 
ing 100  feet.  The  room  pillars  vary  from  6  to  90  feet  in  width  in 
various  mines,  depending  upon  conditions  and  the  methods  adopted 
in  these  mines.  The  pillars  are  much  wider  at  the  stump,  which  lies 
between  the  necks  of  the  rooms  than  elsewhere.  A  common  width  is 
20  to  30  feet  for  these  pillars. 

The  width  of  barrier  pillars,  like  that  of  all  others,  varies  with  the 
conditions,  the  three  main  ones  being  the  inclination  and  depth  of 
the  seam  and  the  amount  of  water  in  the  adjacent  workings.  A  rule 
generally  used  as  a  guide  by  inspectors  and  engineers  in  the  anthracite 
region  of  Pennsylvania  is  as  follows:  Multiply  the  thickness  of  the 
deposit  in  feet  by  i  per  cent  of  the  depth  below  drainage  level  and  add 
to  this  5  times  the  thickness  of  the  bed.  In  the  bituminous  region  of 
Pennsylvania  the  mine  law  fixes  the  width  of  the  pillar  according  to 
the  conditions  relating  to  water  pressure. 

In  some  of  the  steeply  pitching  anthracite  seams  it  is  probably 
impractical  to  attempt  to  leave  a  barrier  pillar  which  will  be  capable 
of  supporting  the  load  and  holding  back  the  water  in  deep  basins, 
when  the  seams  have  been  extensively  mined.  The  oxidation  of 
the  coal  where  circulating  water  comes  in  contact  with  it  tends  to 
weaken  the  pillar  in  time. 

There  are  many  rules  for  establishing  the  size  of  shaft  pillars.  As 
in  the  cases  of  the  other  pillars  mentioned  it  is  necessary  to  leave  a 
large  margin  of  safety  as  it  is  extremely  important  to  protect  the  shaft 
bottom  and  the  structures  on  the  surface  from  any  damage.  Among 
the  rules  for  the  size  of  shaft  pillars  which  are  most  generally  ac- 
cepted is  Dron's,  which  allows  for  a  good  factor  of  safety.  Dron's 
Rule  is  as  follows:  Draw  a  line  enclosing  all  surface  buildings  that 
should  be  protected  by  the  shaft  pillar.  Make  the  pillar  of  such  a  size 
that  solid  coal  will  be  left  over  the  whole  area  enclosed  by  this  line  and 
for  a  distance  beyond  the  line  equal  to  one-third  the  depth  of  the  shaft. 
The  formula  for  computing  the  diameter  of  the  shaft  pillar  by  this 

2d 
rule  is  as  follows:     D  =  s  -\ ,  where  5  is  the  diameter  of  the  circle 

3 


276  MINING  OF  COAL 

or  square  enclosing  the  structure  on  the  surface  and  d  is  the  depth  of 
the  shaft,  in  the  same  units  of  measurement. 

Some  of  the  other  rules  employed  are  as  follows: 

Andre's  Rule :  Minimum  diameter  of  circular  pillar  or  side  of  square 
pillar  should  be  35  yards  to  a  depth  of  150  yards.  Add  5  yards  for  each 
25  yards  of  additional  depth. 

D  =  35  +  5 


Mining  Engineering  Rule:  Radius  of  circular  pillar  or  half  side 
of  square  pillar,  in  yards  is  equal  to  20  yards  plus  one-tenth  of  the  prod- 
uct obtained  by  multiplying  the  depth  of  shaft,  in  yards,  by  the  square 
root  of  the  thickness  of  the  seam  in  yards. 


^        (      ,  d  x  Vt\ 

D  =    2  [  20  H )   = 

V  10     / 


d  x  Vt\            .   d  x  Vt 
40  + 


where  d  =  depth  of  shaft  and  t  the  thickness  of  the  seam. 

Foster's  Rule :  Radius  of  circular  pillar,  or  half  side  of  square  pillar 
in  feet,  is  equal  to  3  times  the  square  root  of  the  product  of  the  depth  of 
cover,  in  feet,  and  the  thickness  of  the  seam  in  feet. 

Hughes  Rule:  For  the  diameter  of  a  circular  pillar  or  the  side  of 
a  square  pillar  allow  i  yard  for  each  yard  in  depth. 

Central  Coal  Basin  Rule:  Leave  100  square  feet  of  coal  for  each 
foot  that  the  shaft  is  deep,  a  main  entry  of  average  width  being  driven 
through  this  pillar.  If  the  bottom  is  soft  the  result  is  increased  by  one- 
half.  

D  =  Vioo  d 

Modifications  of  The  Room-and-Pillar  Method 

The  pillar-and-stall  system.  —  This  system  is  also  known  in  some 
places  as  bord-and-pillar  and  post-and-pillar,  although  the  systems 
are  not  the  same  in  all  respects.  The  pillar-and-stall  system  differs 
from  the  method  already  described  in  the  smaller  size  of  the  rooms  in 
proportion  to  the  size  of  the  pillars.  The  stalls  are  narrow  rooms 
usually  10  to  15  feet  wide  with  pillars  about  the  same  size  in  some 
cases.  In  other  cases  the  rooms  are  driven  about  10  feet  wide  on 
loo-foot  centers  and  the  pillars  are  then  split  a  great  number  of  times. 
In  some  cases  double  stalls  corresponding  to  double  rooms  are  driven. 


ANTHRACITE  MINING  IN  PENNSYLVANIA  277 

This  system  is  used  to  advantage  in  some  seams  with  bad  draw  slate 
and  a  bottom  rock  inclined  to  heave.  In  some  places  the  stalls  are 
driven  full  width  from  the  entry  without  a  neck.  One  form  of  this 
system  is  used  in  the  Connellsville  region  of  Pennsylvania. 

The  panel  system.  —  The  principle  adopted  in  the  panel  system  is 
to  divide  the  area  to  be  mined  into  square  or  rectangular  blocks  by 
entries  driven  at  right  angles  to  each  other,  (Fig.  87).  These  blocks 
are  subdivided  into  a  large  number  of  smaller  blocks  and  thus  the 


FIG.  87.  —  The  panel  system. 

original  section  is  worked  out  as  a  unit.  A  large  solid  pillar  is  usually 
left  surrounding  the  panel  on  three  sides,  serving  as  a  barrier  in  case 
of  fire  or  accident  and  controlling  the  air  circulation.  The  system 
has  the  disadvantage  of  much  narrow  work  but  the  advantage  of 
giving  complete  control  of  the  ventilation  in  that  section  of  the  mine 
and  of  permitting  the  block  to  be  handled  as  a  separate  unit  in  case 
of  accident. 

Anthracite  mining  in  Pennsylvania.  —  Since  special  methods  must 
be  employed  in  seams  dipping  more  than  10°  a  description  of  some  of 
the  methods  employed  in  the  anthracite  region  of  Pennsylvania  will 
serve  to  illustrate  the  main  variations  from  those  employed  in  flat- 
lying  seams.  In  general  the  room-and-pillar  method  is  used,  but  the 
rooms  are  known  as  breasts  or  chambers  and  the  entries  as  headings 


278 


MINING  OF   COAL 


or  gangways.  The  breasts  are  driven  to  the  rise  and  nearly  up  to  the 
next  higher  gangway,  (Fig.  88). 

One  of  the  main  problems  confronting  the  miner  in  inclined  seams 
is  that  of  transporting  the  coal  in  the  breast  from  the  face  to  the  gang- 
way. The  following  methods  are  employed:  If  the  seam  does  not 
pitch  more  than  10  or  12°  and  the  breasts  are  driven  at  an  inclination 

to  the  pitch  the  car  may 
be  taken  to  the  face  and 
lowered  by  hand,  by 
mule  or  motor.  These 
means  cannot  be  em- 
ployed in  a  seam  pitch- 
ing more  than  5  or  6°  if 
the  breast  be  driven  on 
the  full  pitch.  If  the 
breast  be  driven  on  the 
full  pitch  the  car  may 
be  lowered  by  windlass 
up  to  10  or  12°  inclina- 
tion. Jig  roads  are  also 
used  under  similar  con- 
ditions. 

The  buggy  system.  — 
The  buggy  system  is 
often  used  in  thick 
seams  where  there  is 
plenty  of  head  room. 
This  system  consists  in 

the  use  of  a  small  car  which  can  be  taken  to  the  face  by  hand  or  by 
aid  of  a  windlass  where  the  seam  pitches  from  10  to  18°.  The  coal 
is  loaded  on  the  buggy,  taken  down  the  breast  and  dumped  on  a 
platform,  from  which  it  is  shoveled  into  the  mine  car  in  the  gang- 
way. In  some  cases  two  buggies  are  used  and  the  coal  is  trans- 
ferred from  one  to  the  other  and  thus  lowered  by  stages.  This 
method  is  costly  in  labor  and  coal  broken. 

Chutes.  —  In  seams  dipping  between  1 5°  and  30°  the  coal  is 
usually  sent  down  sheet-iron  chutes  to  the  gangway.  These  chutes 
are  laid  in  the  center  of  the  breast  with  a  row  of  props  along  either 


FIG.  88.  —  Mining  anthracite  in  Pennsylvania  in 
steeply  dipping  seam.  (After  H.  H.  Stock,  U.  S. 
Geol.  Survey.) 


CHUTES 


279 


side  and  the  gob  is  stored  between  these  props  and  the  ribs.  The 
men  travel  along  the  chute.  When  the  seam  dips  more  than  30° 
the  coal  will  usually  slide  of  its  own  weight  and  it  is  necessary 
to  place  an  obstruction  at  the  bottom  of  the  chute  in  the  neck  of  the 
chamber  to  hold  the  coal  back.  The  structure  employed  is  known 
as  a  battery,  and  a  breast  with  such  an  arrangement  as  a  battery  breast, 
(Fig.  89):  The  coal  is  drawn  out  through  the  battery  at  such  a 
rate  that  plenty  of  broken  coal  remains  in  the  breast  to  permit  the 
men  to  stand  upon  it  and  work  at  the  face.  This  avoids  the  necessity 
of  building  a  timber  stage  on  which  to  work.  In  some  cases  the 
breasts  are  driven  with  double  necks  and  two  batteries  are  then 

constructed,  (Fig.  90).  This  arrange- 
ment has  the  advantage  where  the  seam 
is  steeply  inclined,  of  leaving  a  large 
pillar  in  the  center  of  the  lower  end  of 


FIG.   89.  —  Single  battery  breast  in  FIG.  90.  —  Double  battery  breast, 

anthracite  mine. 

the  breast  to  support  the  weight  on  the  battery.  In  the  battery 
breasts  a  manway  must  be  provided  as  a  separate  opening  driven 
through  the  coal  or  as  an  opening  through  the  battery.  In  the 
breasts  the  men  travel  along  the  chute  which  is  lined  with  posts 
securely  set  into  the  floor  and  roof  of  the  seam. 

In  the  working  of  contiguous  seams  or  of  seams  lying  parallel  and 


280 


MINING  OF  COAL 


close  together  but  separated  by  more  than  about  3  feet  of  rock,  the 
coal  in  the  upper  seam  is  carried  to  the  gangways  in  the  lower  seam 
through  rock  chutes,  (Fig.  91).  If  there  be  less  than  about  3  feet  of 
rock  separating  the  seams  they  are  usually  worked  as  one  seam  with 
a  parting,  and  the  rock  is  mined  out.  Where  contiguous  seams  are 
worked  the  working  of  the  upper  seam  is  usually  completed  first  and 
the  pillars  robbed  before  the  underlying  seam  is  worked  beyond  the 
driving  of  gangways  and  airways. 


FIG.  91.  —  Method  of  working  contiguous   seams    through    a    horizontal  rock  tunnel. 
(After  H.  H.  Stock,  U.  S.  Geol.  Survey.) 

Pillar  Drawing 

During  the  first  mining  a  large  portion  of  the  coal  is  left  in  the 
pillars  and  it  must  be  extracted  later.  The  process  of  removing  the 
coal  in  the  pillars  is  known  as  robbing  pillars  or  pillar  drawing. 
It  is  one  of  the  more  hazardous  features  of  mining  operations  and 


THE  LONGWALL  METHOD  281 

the  work  should  be  attempted  only  by  the  more  experienced 
miners.  The  percentage  of  coal  left  in  the  pillars  after  the  first  work- 
ing varies  from  30  to  65  per  cent  of  that  originally  in  the  seam,  and 
in  some  cases  where  the  thickness  of  the  seam  is  favorable,  the  gas 
not  excessive,  and  the  roof  and  bottom  good,  as  much  as  98  per  cent 
has  been  removed  by  final  working. 

There  are  several  systems  of  robbing  pillars  and  the  one  adopted 
depends  largely  upon  the  local  conditions.  In  some  cases  a  break- 
through is  made  at  the  inby  end  of  the  pillar  and  the  pillar  is  gradually 
removed  until  only  the  stump  is  left  near  the  entry.  Props  are  used 
to  partially  support  the  roof  as  the  coal  is  removed  and  as  the  work 
advances  the  props  are  recovered  and  the  roof  allowed  to  cave.  Care 
must  be  exercised  in  supporting  the  roof  so  as  to  keep  sufficient  pres- 
sure on  the  coal  to  help  break  it  but  not  enough  to  crush  the  pillar. 
The  roof  should  be  broken  at  the  stumps  if  possible,  so  as  to  relieve 
the  weight  on  the  entry  pillars.  Gas  should  not  be  allowed  to  collect 
in  the  gob  for  an  indefinite  period  as  it  may  escape  into  the  workings 
or  take  fire.  Another  method  of  robbing  pillars  consists  in  splitting 
the  pillars  one  or  more  times  and  then  drawing  them  back  as  described 
above. 

In  some  mines  the  pillars  are  drawn  out  in  panels  and  in  others 
the  workings  are  driven  to  the  edge  of  the  property  and  the  pillars 
drawn  back  on  a  retreating  system.  In  any  case  the  ends  of  the 
pillars  being  drawn  back  should  be  kept  in  a  nearly  straight  line  so 
as  to  keep  the  roof  supported  and  also  to  let  it  cave  in  a  systematic 
manner,  (Fig.  84).  This  lessens  the  danger  to  the  miners  and  avoids 
the  loss  of  coal. 

THE  LONGWALL  METHOD 

There  are  two  main  systems  in  longwall  mining  and  several  modi- 
fications of  these  systems  to  suit  particular  conditions.  The  systems 
are  known  as  the  advancing  and  retreating  systems.  In  the  former 
the  workings  are  advanced  from  the  shaft  pillar  toward  the  border 
of  the  property  and  in  the  latter  the  main  entries  are  driven  to  the 
border  of  the  property  and  the  workings  are  then  carried  back  toward 
the  main  shaft.  The  main  features  of  the  longwall  method  are  the  re- 
moval of  practically  all  of  the  coal  as  the  face  advances  and  the  main- 
taining of  a  continuous  working  face  around  the  workings,  (Fig.  92). 
The  waste  rock  is  used  to  fill  up  the  space  from  which  the  coal  has  been 


282  MINING  OF   COAL 

removed  and  the  roadways  are  maintained  by  pack-walls  on  either 
side  of  them,  made  of  waste  rock.  These  piles  of  rock  are  known  as 
the  road  packs  and  those  in  the  areas  between  the  roads  as  gob  packs. 
The  main  roads  run  diagonally  from  the  shaft  pillar  like  the  spokes  of 
a  wheel,  and  the  intervening  areas  are  subdivided  into  smaller  and 
smaller  sectors  by  subsidiary  roads. 


Overcasts  shown  thus:   X 
Curtains  shown  thus ;     — 

FIG.  92.  —  Plan  of  a  longwall  mine  showing  direction  of  ventilating   current.     (After 
Swift;    from  Bull.  13,  III.  Geol.  Survey,  University  of  111.  and  U.  S.  Bur.  of  Mines.) 

In  this  method  little  of  the  coal  is  blasted  from  the  face,  the  roof 
pressure  being  used  to  break  it  down  after  the  coal  is  undercut.  It 
is  necessary  therefore  that  the  face  be  advanced  uniformly  and  con- 
tinuously. 

This  method  is  particularly  adapted  to  thin  seams  where  the  roof 
settles  and  the  bottom  tends  to  heave,  since  the  waste  rock  is  used 
for  packing  and  the  coal  can  all  be  removed  in  the  first  working. 
It  also  leaves  the  surface  in  better  condition  than  the  room-and- 


THE   LONGWALL  METHOD 


283 


pillar  method  because  the  strata  settle  more  uniformly.  A  larger 
percentage  of  the  coal  can  be  extracted  in  most  cases  than  with  the 
other  system.  Less  timber  is  needed  for  roadways  than  in  other 
methods  and  as  a  rule  this  method  brings  quicker  return  for  capital 
and  labor. 


FIG.  93.  —  Plan  of  longwall  mine  with  auxiliary  permanent  entries.   (After  S.  O.  Andros.) 

The  disadvantages  of  the  longwall  method  lie  in  the  fact  that  more 
experienced  miners  are  needed  to  operate  the  mine  successfully.  A 
section  of  the  mine  cannot  be  controlled  as  with  the  other  methods 
and  the  mine  suffers  more  from  idleness  or  from  irregular  work  of 
men  at  the  face.  It  is  more  difficult  to  get  into  operation  and  a  great 
deal  of  trouble  is  often  encountered  in  getting  the  roof  to  break  prop- 
erly around  the  shaft  pillar  or  at  the  limits  of  the  property  as  the  case 
may  be.  It  is  only  successful  where  there  is  plenty  of  waste  rock, 
although  in  France  it  is  employed  where  rock  must  be  brought  in 


284 


MINING   OF   COAL 


from  the  surface  in  great  quantities.  There  are  immense  quarries 
in  central  France  from  which  the  rock  is  taken  for  this  purpose, 
(Fig.  96).  This  increases  the  expense  considerably.  In  the  United 
States  the  longwall  method  is  used  comparatively  little.  There  are 
a  good  many  longwall  mines  in  Colorado  and  some  of  the  other  west- 
ern states,  a  number  in  Illinois  and  a  few  in  some  of  the  eastern 
states.  Certain  modified  systems  used  in  the  anthracite  region  of 
Pennsylvania  are  known  as  the  chamber  longwall,  lateral  longwall  and 
block  longwall  systems.  These  are  operated  on  a  rectangular  or  sort 
of  panel  arrangement,  (Figs.  94  and  95). 


Gangway 

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Airway  in  Coal  Only                                                                  |»_ 

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Pillar  Left  in  Place 

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Gangway^ 

p    a 

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Airway  in  Coal  Only 

FIG.  94.  —  Block  longwall  system.     (By  courtesy  of  the  D.  &  H.  Company, 

Scranton,  Pa.) 

Mining  in  thick  seams.  —  When  seams  are  very  thick  it  is  neces- 
sary to  mine  them  in  benches  or  with  some  sort  of  shrinkage  stope 
system.  The  system  which  has  been  most  successful  is  a  modified 
form  of  the  longwall  in  which  the  seam  is  worked  in  benches  and  the 
open  spaces  packed  full  of  waste  rock,  (Fig.  97). 

Breaking  the  Coal  at  the  Face 

Several  methods  are  employed  in  breaking  the  coal  at  the  face. 
When  the  longwall  method  of  mining  is  adopted  the  coal  is  undercut 


BREAKING  THE  COAL  AT  THE  FACE  285 

by  a  longwall  machine  and  the  roof  is  allowed  to  settle  gradually  so 
as  to  break  down  the  coal.  In  the  room-and-pillar  method  the  coal 
is  undercut  by  a  coal  cutting  machine  or  by  miners'  picks  and  is  blasted 
or  wedged  down,  (Fig.  98).  In  many  cases  the  coal  is  sheared  as 
well  as  undercut.  Shearing  consists  in  making  a  vertical  cut  along 
the  side  of  the  room  or  entry  as  the  case  may  be  in  order  to  keep  the 
wall  straight  and  uniform.  Some  of  the  latest  machines  will  not 


FIG.  95.  —  Development  of  a  longwall  operation  in  the  anthracite  region. 
(By  courtesy  of  the  D.  &  H.  Company,  Scran  ton,  Pa.) 


only  undercut  the  coal  but  also  shear  it,  and  it  is  expected  that  in  the 
near  future  they  will  be  so  constructed  that  they  will  also  success- 
fully break  down  the  coal.  The  depth  of  the  channel  which  is  cut 
along  the  bottom  of  the  seam,  or  along  a  parting  in  the  coal  as  the 
case  may  be,  may  reach  6  feet  or  more,  but  it  depends  somewhat  upon 
the  nature  of  the  coal  and  roof  pressure.  When  it  is  done  by  hand  it 
must  be  wide  enough  to  permit  a  man  to  lie  in  it  on  his  side  and  work 


286  MINING  OF  COAL 

a  pick,  the  seam  above  him  being  kept  from  closing  down  by  a  short 
prop.  After  the  coal  is  undercut  it  is  shot  down  or  wedged  down. 
In  some  cases  coal  is  shot  from  the  solid,  and  fhis  is  necessary  in 
many  anthracite  mines.  This  method  has  the  disadvantage  of 
breaking  the  coal  up  so  that  much  more  slack  and  less  lump  coal 
results.  There  is  also  more  danger  in  firing  owing  to  the  heavy 
charges  necessary  to  blow  the  coal  down.  The  production  of  a 
greater  percentage  of  slack  does  not  matter  so  much  if  it  is  to  be 
used  for  coking  but  it  lowers  the  value  of  the  coal  very  greatly  for 
domestic  and  steaming  purposes.  A  great  deal  of  care  and  judg- 
ment is  necessary  in  placing  the  holes  which  are  made  by  augers  or 
hammer  drills,  as  their  depth  and  arrangement  affect  the  amount  of 
coal  shot  down,  the  conditions  in  which  the  broken  coal  occurs  and 
the  safety  of  the  miners,  especially  when  black  powder  is  used. 

Mining  Machines 

There  has  been  a  rapid  development  in  coal  mining  machines  in 
recent  years.  The  latest  coal-cutter  has  been  so  developed  that  it  can 
undercut  and  shear  the  seam,  can  cut  out  a  sulphur  band  or  a  parting 
in  the  seam  and  can  be  operated  much  more  readily  than  the  earlier 
types.  There  are  also  loading  machines  which  apparently  work 
quite  successfully  under  certain  conditions.  The  tendency  has  been 
to  get  away  from  the  pick  machines,  or  punchers  and  adopt  the  con- 
tinuous cutting  types.  The  application  of  electricity  has  been  re- 
sponsible for  a  great  development  in  mining  machines  and  it  is  now 
possible  to  use  electric  machines  in  gaseous  mines.  According  to  the 
latest  report  of  the  Department  of  Mines  of  Pennsylvania,  the  per- 
centage of  bituminous  coal  mined  in  this  state  by  compressed  air 
machines  in  the  year  1899  was  21.22,  and  in  1917  it  was  9.03.  In  the 
same  years  the  percentages  mined  by  electrical  machines  were  18.38 
and  45.14  respectively.  In  the  same  years  the  percentages  mined  by 
hand  were  60.40  and  45.83. 

The  use  of  cutting  machines  in  the  anthracite  region  has  developed 
more  slowly  than  in  the  bituminous  region  of  Pennsylvania,  owing 
to  the  difficulty  in  cutting  the  harder  coal  and  in  moving  the  machines 
on  the  steep  pitches,  but  the  machines  are  now  successfully  used  in 
parts  of  the  region. 


MINING  METHODS  IN  FOREIGN  COUNTRIES 


287 


It  seems  probable  that  we  will  see  a  machine  in  the  not  far  distant 
future  which  will  undercut,  shear,  break  down  and  load  the  coal 
where  the  conditions  are  favorable. 

Mining  Methods  in  Foreign  Countries 

Europe.  —  The  longwall  method  is  much  more  generally  used  in 
Europe  than  in  America,  and  on  the  European  continent  it  is  used 
almost  entirely.  According  to  G.  S.  Rice1  the  typical  American  room- 
and-pillar  method  is  not  used  in  Europe  except  in  a  few  places  in 
Wales,  where  it  is  known  as  the  pillar-and-  (single) -stall  method,  and 


FIG.  96.  —  Open  cut  at  Commentry,  France,  from  which  coal  has  been  mined  and  most 
of  the  rock  used  to  fill  the  mines.     (Photo  by  E.  S.  Moore.) 

in  Upper  Silesia  where  it  was  formerly  used  rather  extensively  but  is 
now  largely  abandoned  for  the  longwall  method.  The  pillar-and- 
double-stall  method  was  formerly  used  to  some  extent  in  Scotland 
and  in  Wales  but  it  has  also  been  nearly  abandoned  for  the  longwall 
method.  In  South  Staffordshire  a  method  known  as  the  square- 
chamber  method  has  been  used  in  the  Ten  Yard  seam.  In  this  method 
the  coal  is  worked  by  chambers  46  yards  wide  and  up  to  200  feet  long 
with  thick  pillars  between  them.  Four  to  six  coal  pillars  are  left 
standing  in  rows  through  the  chamber. 

1  Rice,  G.  S.,  Coal-pillar  drawing  methods  in  Europe.     Trans.   Amer.  Inst.  Min. 
Met.  Eng.,  New  York  Meeting,  Feb.  1921. 


288  MINING  OF  COAL 

The  bord-and-pillar  or  stoop-and-room  method  is  common  in  the 
north  of  England,  in  Scotland  and  to  a  lesser  extent  in  Wales.  In 
Upper  Silesia  it  is  used  in  a  modified  form  where  the  hydraulic  sand 
filling  system  is  in  use  in  the  thick  seams.  The  writer  has  visited 
mines  near  St.  Etienne,  France,  where  the  modified  longwall  method 
was  being  used  and  the  waste  rock  of  the  mine  was  supplemented  by 
rock  brought  in  from  the  surface  so  that  the  space  mined  out  could 
be  completely  filled  up  as  fast  as  the  coal  was  removed,  (Fig.  96). 

Australia.1  —  On  this  continent  the  pillar-and-bord  system  is  very 
largely  used  although  the  longwall  method  is  found  in  a  number  of 
mines.  In  several  places  both  methods  are  used  in  the  same  mine. 


.. 

FIG.  97.  —  Bench  working  in  thick  seams,  with  stone  packs. 

. 

E  » 

In  some  mines  one  method  is  used  in  one  seam  and  the  other  method 
in  an  underlying  seam,  depending  upon  the  thickness  of  the  coal,  the 
abundance  of  waste  rock  and  other  factors. 

Mine  Haulage 

Haulage  in  mines  is  performed  by  animals,  electric  motors,  com- 
pressed air  locomotives,  steam  locomotives  and  cables.  There  are  ad- 
vantages in  all  these  sources  of  power  under  certain  conditions.  Some 
companies  have  successfully  taken  the  cars  to  and  from  the  face  with 
a  motor  while  others  have  found  it  uneconomical  to  use  a  motor  for 
other  purposes  than  hauling  trains  of  mine  cars  considerable  dis- 
tances. In  the  latter  case  a  mule  is  used  for  gathering  the  cars  into 
trains.  Whether  a  motor  may  be  used  successfully  in  gathering  seems 
to  depend  very  largely  upon  the  thickness  of  the  seam  and  the  ease 
with  which  the  tracks  are  kept  open  and  in  good  condition. 

Rope  or  cable  haulage  is  of  two  types,  endless  and  tail.     In  the 

1  Power,  F,  Danvers,  Coalfields  and  collieries  of  Australia.     1912. 


HOISTING  289 

former  type  the  cable  runs  continuously  and  the  car  is  arranged 
so  as  to  grip  the  cable.  This  works  successfully  in  some  mines  but 
unsuccessfully  in  others.  The  straightness  and  regularity  of  the 
entries  has  a  good  deal  of  influence  on  this  system.  With  the  tail 
rope  the  cars  are  hauled  in  opposite  directions  by  separate  ropes. 

Conveyors  are  now  being  used  successfully  in  some  mines,  espe- 
cially in  some  of  the  thin  seams  in  the  anthracite  region  of  Pennsyl- 
vania. Scrapers  have  also  been  used  to  some  extent  in  gathering 


FIG.  98.  —  Sullivan  Ironclad  alternating  current  mining  machine  in  operation 
undercutting  a  seam.     (By  courtesy  of  the  Sullivan  Machinery  Co.) 

coal.  A  remarkable  conveyor,  about  eight  miles  in  length  is  being 
installed  by  the  H.  C.  Frick  Company  for  transporting  to  the  river 
the  coal  from  several  mines.  It  runs  underground  and  the  great  belt 
is  driven  by  a  series  of  motors  connected  with  each  other  by  auto- 
matic control  systems.  It  may  revolutionize  this  type  of  trans- 
portation. 

Hoisting 

Hoisting  of  coal  is  usually  accomplished  by  raising  the  mine  car  to 
the  tipple  and  dumping  it.     Some  mines,  however,  have  operated 


2  go 


MINING  OF   COAL 


lo-ton  skips  very  successfully.1  Some  of  the  advantages  claimed  for 
skip  hoisting  over  a  self-dumping  cage  are:  a  larger  capacity  for 
coal  and  rock;  smaller  shaft  necessary;  lower  rope  speed  and  power 
consumption;  and  fewer  men.  Some  of  the  objections  commonly 
made  to  skip  hoisting  are:  the  greater  breakage  of  coal,  although 
this  does  not  appear  to  be  necessary;  excessive  dust  raised  by  dumping 
at  bottom  of  shaft;  necessity  of  a  cage  for  hoisting  men  and  materials; 
difficulty  in  docking  and  inspecting  the  coal;  and  difficulties  in  hand- 
ling waste  rock  on  the  surface. 


FIG.  99.  —  Electric  haulage.     A  trip  leaving  the  mine  of  the  Ebensburg  Coal  Company. 
(Photo,  by  courtesy  of  J.  F.  Macklin,  Pres.  Ebensburg  Coal  Co.) 


Mine  Gases2 

Ordinary  pure  air  contains  about  20.93  Per  cent  by  volume  of 
oxygen,  79.04  per  cent  nitrogen,  3  parts  in  10,000  of  carbon  dioxide 
and  small  amounts  of  argon,  helium  and  other  gases.  Water  vapor  is 
present  in  varying  amounts  depending  upon  temperature  and  pressure 
and  the  presence  of  water  in  the  neighborhood.  The  oxygen  is  the 
most  active  chemical  agent  in  the  atmosphere  and  it  unites  with 

1  Allen,  A.,  and  Garcia,  J.  A.,  Skip  hoisting  for  coal  mines.     Trans.  Amer.  Inst. 
Min.  and  Met.  Eng.,  New  York  Meeting,  Feb.  1921. 

2  Beard,  J.  T.,  Mine  gases  and  explosions.    John  Wiley  &  Sons,  Inc.,  1908. 


CARBON  DIOXIDE  291 

metals  causing  them  to  deteriorate,  as  in  the  case  of  iron  rusting. 
Oxygen  is  given  off  by  plants,  but  when  animals  breathe  slow  com- 
bustion occurs  as  in  a  fire  and  the  carbon  in  their  systems  unites  with 
the  oxygen  to  produce  carbon  dioxide.  Nitrogen  is  an  inert  gas  and 
serves  the  purpose  of  diluting  the  oxygen  of  the  air. 

In  some  mines  the  air  is  fairly  pure  and  an  open  light  may  be 
carried  without  danger.  In  others  there  is  an  abundance  of  methane 
and  carbon  dioxide  and  dangerous  quantities  of  carbon  monoxide 
and  hydrogen  sulphide,  making  it  unsafe  to  enter  the  mine  at  all 
with  an  open  light  and  dangerous  to  enter  it  with  a  closed  light  unless 
the  ventilation  is  good. 

Carbon  dioxide.  —  Carbon  dioxide  (CO2)  has  a  molecular  weight 
of  44  and  a  specific  gravity  of  1.529.  Being  heavier  than  air  it  natur- 
ally settles  to  lower  levels  when  with  lighter  gas,  and  this  explains 
why  animals  may  be  overcome  in  low  places  where  this  gas  has  col- 
lected while  at  higher  points  in  the  same  region  they  may  be  quite 
safe.  It  should  be  borne  in  mind,  however,  that  this  may  not  always 
be  true  for  the  location  of  the  gas  in  mines  since  the  air  currents  and 
the  source  of  the  gas  may  have  some  influence  on  its  gathering  point. 
It  is  a  product  of  combustion  from  fire  and  the  lungs  of  animals.  It 
may  also  be  given  off  during  the  decay  of  vegetal  matter  and  this 
explains  the  presence  of  a  considerable  amount  of  it  in  the  mines  where 
oxidation  of  the  coal  is  in  progress  and  where  it  has  been  imprisoned 
in  the  coal  seam  since  its  formation  from  the  altering  vegetal  matter. 
A  certain  amount  is  given  off  by  the  breathing  of  the  men  and  the 
horses  or  mules  in  the  mine  and  by  the  burning  of  the  lamps. 

Black  damp  or  choke  damp  is  a  mixture  consisting  chiefly  of  nitro- 
gen and  carbon  dioxide  with  a  little  oxygen.1  It  is  not  explosive  or 
poisonous  but  its  danger  lies  in  the  fact  that  it  excludes  the  oxygen 
so  that  a  sufficient  quantity  does  not  reach  the  lungs  of  animals. 
According  to  W.  G.  Duncan,  average  black  damp  contains  85  to  95 
per  cent  nitrogen  and  the  remainder  is  chiefly  carbon  dioxide.  The 
average  composition  of  the  mixture  is  about  90  per  cent  nitrogen 
and  10  per  cent  carbon  dioxide.  It  is,  therefore,  impossible  for  an 
animal  to  live  or  a  light  to  burn  in  this  gas. 

The  presence  of  carbon  dioxide  may  be  detected  by  an  ordinary 

1  Burrell,  G.  A.,  Robertson,  I.  W.,  and  Oberfell,  G.  G.,  Black  damp  in  mines.  U.  S. 
Bur.  Mines,  Bull.  105,  1916. 


2Q2 


MINING  OF  COAL 


lamp  or  candle  which  requires  17  per  cent  of  oxygen,  but  an  acety- 
lene lamp  is  not  extinguished  until  the  oxygen  is  reduced  to  about  12 
per  cent.  When  3  to  4  per  cent  of  the  dioxide  is  present  most  people 
begin  to  feel  its  effects  in  headaches  or  other  derangements,  and  real 
distress  may  be  caused  by  5  to  6  per  cent  of  the  gas  in  the  air.  Where 
carbon  dioxide  is  present  owing  to  exhalation  of  animals  it  is  not  only 
this  gas  which  causes  the  trouble  but  also  the  deficiency  in  the  oxy- 
gen which  has  been  removed  by  breathing. 


FIG.  ioo.  —  Shaft  bottom  of  Jerome  Shaft  No.  2.     Hillman  Coal  and  Coke  Co. 
(By  courtesy  of  the  Hillman  Coal  and  Coke  Co.) 


Carbon  monoxide.  —  Carbon  monoxide  (CO)  is  an  odorless,  color- 
less gas  with  a  molecular  weight  of  28,  a  density  of  14,  and  a  specific 
gravity  0.967.  It  is,  therefore,  slightly  lighter  than  air.  Its  rate  of 
diffusion  compared  with  air  is  1.0149  and  its  ignition  point  650°  C. 
When  mixed  with  air  in  any  proportions  it  forms  white  damp.  Un- 
like carbon  dioxide  it  is  a  deadly  poison,  the  effects  in  some  cases  being 
sudden,  in  other  cases  delayed.  It  requires  only  about  TV  of  i  per 


CARBON  MONOXIDE 


293 


cent  of  this  gas  in  air  to  cause  dizziness,  headache,  shortness  of  breath 
or  other  effects,  and  T\  may  be  dangerous,  while  T\  of  it  is  almost  sure 
to  be  fatal.  The  gas  attacks  the  haemoglobin  of  the  blood  and  60 
to  70  per  cent  saturation  of  the  blood  is  fatal.  It  usually  takes  from 
5  to  6  hours  to  free  the  blood  after  a  serious  case  of  poisoning.  The 
effect  on  the  blood  is  to  turn  it  a  pink  color.  The  best  treatment  is  to 
remove  the  patient  into  pure  air  and  apply  heat  to  the  body  by  wrap- 
ping up  in  warm  blankets  or  applying  hot-water  bottles.  In  serious 
cases  of  poisoning  it  may  be  necessary  to  use  pure  oxygen  mixed  with 
10  per  cent  CC>2.  To  test  mine  gas  for  the  presence  of  CO  a  small 
animal  such  as  a  mouse  or  canary  bird  is  used,  the  latter  being  the  best 
indicator.  Experiments  by  the  United  States  Bureau  of  Mines1  have 
shown  that  in  air  containing  carbon  monoxide  canaries  and  mice  be- 
haved as  follows: 

TABLE  SHOWING  THE  EFFECT  OF  CARBON  MONOXIDE 
ON  ANIMALS 


Percentage 
in  air 

Canaries 

Mice 

Chickens 

Dogs 

Guinea  pigs 

O.IO 

No.  tested  8; 
i  affected  in 
12  min.,  2 
slightly  af- 
fected in  4 
hours. 

No.  tested  7; 
i  distressed 
in  30  min.,  6 
showed  no 
distress  in  2\ 
hours. 

No.  tested  i; 
no  effect  in 
2\  hours. 

0.15 

No.  tested  4; 
affected  in  5 
to  30  min. 

No.   tested   i; 
affected    in 
45  min. 

No.  tested  i; 
no  distress  in 
45  min. 

O.2O 

No.  tested  12; 
i  distressed 
in  35  min.,  n 
in  2  to  6  min. 

No.  tested  6; 
i  distressed 
in  40  min.,  5 
in  6  to  1  2  min. 

No.  tested  4; 
distressed  in 
10  to  45  min. 

No.  tested  i; 
slightly 
distressed 
in  5  min. 

o-35 

No.  tested  2; 
i  distressed 
in  i  min.,  i 
in  2  min. 

No.  tested  2; 
i  distressed 
in  2  min.,  i 
in  3  min. 

No.  tested  i; 
distressed 
in    4    to    9 
min. 

0.50 

No.  tested  8; 
distressed 
in    2    to    9 
min. 

It  is  evident  that  all  animals  of  the  same  species  are  not  affected  to 
the  same  degree.     If  an  animal  becomes  accustomed  to  small  amounts 

1  Burrell,  G.  A.,  Seibert,  F.  M.,  and  Robertson,  I.  W.,  Effects  of  carbon  monoxide  on 
small  animals.    U.  S.  Bur.  of  Mines,  Tech.  Paper  62,  1914. 


294  MINING  OF   COAL 

of  the  gas  it  is  more  resistant  to  future  attacks.  Small  animals  are 
more  readily  affected  than  human  beings  but  not  in  proportion  to 
their  weight.  The  flame  of  a  safety  lamp  is  not  affected  by  less  than 
i  J  per  cent  of  this  gas  and  about  2  per  cent  is  necessary  to  show  a  cap. 
This  cap  is  similar  to  that  of  marsh  gas.  An  instrument  known  as 
the  M-S-A  Carbon  Monoxide  Detector  has  recently  been  put  on  the 
market;  it  is  very  sensitive  to  this  gas  and  is  supposed  to  indicate 
within  ten  seconds  any  percentage  of  the  gas  from  0.05  to  i.  Car- 
bon monoxide  is  explosive  when  mixed  with  air  in  proportions  of  about 
I5-5  to  75  per  cent,  but  the  presence  of  carbon  dioxide  and  marsh 
gas  affects  these  limits  by  respectively  raising  and  lowering  them. 

Carbon  monoxide  is  formed  by  incomplete  combustion  of  carbon 
in  a  fire  when  the  oxygen  supply  is  deficient,  by  the  explosion  of  some 
types  of  blasting  powder  such  as  those  deficient  in  saltpetre  and  by 
the  partial  oxidation  of  organic  material.  The  first  process  is  the 
most  important  producer  of  the  gas. 

Methane.  —  This  gas  is  also  known  as  marsh  gas  (CH4),  and  when 
mixed  with  air  it  forms  fire  damp.  Its  molecular  weight  is  16  and  its 
specific  gravity  0.53.  It  is  thus  much  lighter  than  air.  It  is  non- 
poisonous,  tasteless,  odorless  and  colorless.  It  will  not  support  com- 
bustion but  it  will  burn  with  oxygen,  producing  water  and  carbon 
dioxide,  when  the  proportions  of  the  gas  vary  from  i  volume  of  gas 
to  between  3.5  and  30  volumes  of  air,  the  greatest  explosive  intensity 
being  reached  when  the  proportions  are  i  volume  of  methane  to  9.5 
volumes  of  air.  The  cap  produced  on  the  flame  of  a  safety  lamp  is 
the  means  usually  employed  in  detecting  the  presence  of  the  gas  and 
the  following  table  shows  how  the  cap  develops  with  the  varying  per- 
centages of  the  gas  present  in  the  air : 

Percentage  of  methane  Height  of  cap  and  flame 

i Base  of  cap  forming 

1 2 iinch 

2 f  to  2  inch 

25 |  inch  and  slightly  luminous  top 

2f finch 

3 i  j  inches 

35 15  to  if  inches 

3f Up  in  gauze 

An  increase  in  moisture  lowers  the  explosibility  of  fire  damp  and  a 
mixture  of  i  part  of  carbon  dioxide  with  7  parts  of  an  explosive  mixture 


SAFETY  LAMPS  295 

of  air  and  marsh  gas  makes  it  non-explosive,  or  i  part  of  nitrogen  to 
6  parts  of  a  similar  mixture  produces  the  same  result. 

Marsh  gas  is  abundant  in  some  mines  but  almost  entirely  absent 
in  others.  It  is  given  off  by  the  coal  and  it  results  from  the  alter- 
ation of  the  vegetal  matter  in  forming  coal  as  indicated  in  a  general 
way  in  the  following  equation: 

C57H56010  -  (3H20  +  C02  +  2CH4)  =  C^A 

Lignite  Bituminous  coal 

As  previously  mentioned,  one  mine  in  the  anthracite  region  of  Penn- 
sylvania has  produced  as  much  as  2400  cubic  feet  of  methane  per 
minute.  (For  further  notes  see  discussion  of  gases  under  the  Chemi- 
cal Properties  of  Coal,  Chapter  II.) 

Hydrogen  Sulphide.  —  Hydrogen  sulphide,  or  sulphuretted  hy- 
drogen (H2S)  occurs  in  mines  in  small  amounts  and  when  it  is  mixed 
with  air  the  mixture  is  known  as  stink  damp  or  stone  damp  since  it 
has  a  very  strong  and  disagreeable  odor.  It  results  in  very  small 
amounts  from  blasting,  especially  where  black  powder  is  used  and 
it  is  also  set  free  through  the  decay  of  organic  matter.  The  odor  of 
rotten  eggs  is  largely  due  to  the  presence  of  this  gas.  It  may  also 
be  generated  by  the  action  of  acids  on  sulphur  compounds.  The  gas 
will  not  support  combustion  but  it  burns  in  air  with  a  pale  blue  flame, 
the  temperature  of  ignition  being  333.3°  C.  or  at  red  heat.  When 
mixed  with  one-half  times  its  own  volume  of  air  it  burns  with  ex- 
plosive force  and  with  7  volumes  of  air  it  explodes  violently.  It 
produces  headache,  nausea  and  the  loss  of  the  sense  of  smell,  and  if 
inhaled  in  sufficient  quantities  results  are  fatal.  The  amount  neces- 
sary to  produce  death  in  a  human  being  is  about  i  part  by  volume  to 
200  parts  of  air.  Canary  birds  are  sensitive  to  about  .05  per  cent  in  air. 
Treatment  consists  in  removal  to  a  plentiful  supply  of  fresh  air,  and  in 
severe  cases  a  little  chlorine  gas  may  be  administered  to  aid  recovery. 

Hydrogen.  —  This  gas  may  be  formed  in  small  amounts  in  mines  as 
a  result  of  incomplete  combustion  in  mine  fires  or  in  explosions,  but 
it  seldom  occurs  in  noticeable  quantities.  Other  rarer  gases,  including 
some  of  the  paraffin  series,  occur  in  very  small  quantities  in  mines. 

Safety  Lamps 

Various  methods  have  been  devised  for  the  lighting  of  mines,  from 
the  torch  and  the  flint  mill  which  generated  sparks  by  contact  of  a 


296  MINING  OF   COAL 

steel  wheel  with  a  piece  of  flint,  to  the  high  candle  power  electric  light 
of  the  present  day.  In  gaseous  mines  it  is  necessary  to  have  a  closed 
light  and  this  gave  rise  to  the  safety  lamp  which  is  now  found  in  such 
great  variety.  The  structure  of  the  safety  lamp  is  based  on  the  prin- 
ciple of  a  protecting  envelope  through  which  air  will  pass  but  which 
will  prevent  the  gases  outside  of  the  lamp  from  becoming  heated  to 
the  temperature  of  ignition.  The  first  safety  lamp  was  invented  by 
Clanney  in  1813  and  air  was  forced  into  it  through  a  water  seal  by 
means  of  a  bellows.  The  Davy  safety  lamp  was  invented  by  Sir 
William  Davy  two  years  later  and  had  a  wire  gauze  around  the  flame 
to  conduct  the  heat  away  so  that  the  gases  outside  of  the  lamp  would 
not  take  fire.  Credit  is  also  due  to  George  Stephenson  for  discovering 
the  principle  of  the  bonnet  'the  same  year.  The  modern  lamps  are 
safely  locked  so  that  a  miner  cannot  unlock  them  in  the  mine  but  must 
take  them  to  a  safe  place  to  be  unlocked  by  a  key  or  an  electrical 
device.  Most  of  them  have  a  self-lighting  device  inside  which  in- 
sures greater  safety  to  the  men.  Oil  is  the  fuel  mostly  used.  The 
light  is  much  better  in  the  modern  lamp  than  in  the  older  types  since 
it  has  a  glass  envelope  or  chimney  and  the  air  enters  near  the  base  of 
the  lamp. 

The  electric  cap  lamp  has  made  its  appearance  in  the  mines  during 
the  last  seven  years  and  it  gives  promise  of  being  very  largely  used 
because  of  its  greater  convenience  and  its  efficiency  in  producing  light.1 
It  has  one  serious  objection  to  the  miner  used  to  the  other  safety  lamps, 
and  that  is  the  fact  that  it  does  not  indicate  the  presence  of  harmful 
gases. 

For  open  lights  in  non-gaseous  mines  acetylene  generated  from 
calcium  carbide  in  contact  with  water  produces  a  very  efficient  light 
and  acetylene  lights  are  very  commonly  used. 

Mine  Ventilation 

Since  a  coal  mine  is  certain  to  contain  more  or  less  foul  air  it  is 
essential  that  it  be  well  ventilated.  There  are  two  means  of  ven- 
tilating a  mine:  by  a  furnace  and  by  a  fan.  A  furnace  may  be  used 
in  the  smaller  mines  which  are  not  gaseous.  It  is  built  of  brick  at 
the  foot  of  a  shaft  on  the  main  airway,  so  as  to  create  a  strong  upward 

1  Clark,  H.  H.,  Permissible  electric  lamps  for  mines.  U.  S.  Bur.  of  Mines.  Tech. 
Paper  75,  1914. 


MINE  VENTILATION  297 

draft  by  convection  currents  generated  by  a  fire  which  is  kept  burning 
all  the  time  men  are  at  work  in  the  mine. 

Mine  fans  are  of  many  types.  They  may  be  constructed  as  the  disc 
fan  where  the  blades  are  arranged  as  they  are  on  a  windmill  or  as  the 
centrifugal  type  in  which  the  blades  are  normal  to  the  plane  of  revo- 
lution. The  fans  are  usually  run  so  that  they  propel  the  air  through 
the  airways  and  to  all  the  working  places  in  the  mine,  but  in  some 
cases  the  fan  may  be  run  as  an  exhaust  fan.  It  is  considered  neces- 
sary to  so  ventilate  a  mine  that  every  man  may  have  a  minimum  of 
150  cubic  feet  of  air  per  minute  if  the  mine  be  non-gaseous  and  200 
cubic  feet  if  it  be  gaseous.  The  velocity  of  the  current  of  air  in  the 
mine  workings  is  measured  by  an  anemometer  and  the  pressure  by  a 
water  gage.  If  the  anemometer  reading  were  1800  feet  in  three 
minutes  and  the  size  of  the  airway  6  feet  by  10  feet  the  volume  of  air 

passing  through  would  be  found  in  the  following  way:  6  x  10  X  - 

o 

=  36,000  cubic  feet  per  minute.  Fans  are  as  much  as  35  feet  in  diam- 
eter and  they  are  capable  of  delivering  from  a  few  thousand  up  to  over 
400,000  cubic  feet  of  air  per  minute,  depending  upon  the  size  and  type 
of  the  fan,  the  rate  at  which  it  is  run,  and  the  mine  resistance. 

In  ventilating  a  mine  the  foul  air  and  explosive  gases  are  driven  out, 
but  the  fresh  supply  of  oxygen  tends  to  oxidize  the  coal  and  to  set 
methane  free,  sometimes  at  a  rapid  rate.  The  air  entering  the  mine 
becomes  warmed  and  the  presence  of  air  with  the  increased  tempera- 
ture aids  the  absorption  of  moisture  which  is  carried  out  with  the  air 
current,  leaving  the  mine  dry  and  in  some  cases  dusty.  The  fine  coal 
dust  becomes  distributed  through  the  air  and  acts  much  the  same 
as  an  explosive  gas  when  ignited.1  It  has  been  shown  that  the  dust 
is  capable  of  producing  tremendous  explosions  and  it  is  particularly 
dangerous  when  mixed  with  gas  as  this  increases  the  possibility 
of  igniting  the  dust  by  lamps  or  blasts.  The  discovery  of  the  ready 
explosibility  of  coal  dust  has  aided  greatly  in  avoiding  many  bad  ac- 
cidents. The  danger  of  explosions  may  be  greatly  lessened  by 
sprinkling  the  mine,  and  taking  other  precautions  against  trouble 
such  as  regulating  the  use  of  certain  explosives,  like  black  powder 
which  generates  a  long  flame  on  firing.  There  are  certain  explosives 

1  Rice,  G.  S.,  and  others,  Explosibility  of  coal  dust.    U.  S.  Geol.  Survey,  Bull.  20, 1911. 


298  MINING  OF   COAL 

designated  as  permissible  explosives1  for  coal  mines  and  the  use  of 
these  has  aided  in  reducing  accidents  although  they  are  not  always 
the  most  suitable  from  the  practical  standpoint  for  producing  the  best 
type  of  coal  for  the  market.  Great  strides  have  been  made  in  recent 
years  in  the  direction  of  greater  protection  for  life  and  property  in  coal 
mining  and  the  percentage  of  accidents  has  been  greatly  reduced. 
Mining  has  become  a  relatively  safe  occupation. 

Mine  Fires 

Mine  fires  are  one  of  the  great  causes  of  trouble  in  coal  mines  and 
they  start  by  lamps  firing  gas,  timbers  or  coal,  or  from  blasts  or  spon- 
taneous combustion.  If  they  are  taken  in  their  incipient  stages  they 
can  as  a  rule  be  put  out  although  the  safest  practice  is  to  take  all 
precautions  against  letting  them  get  started.  When  small  they  may 
be  put  out  with  water  or  a  chemical  extinguisher  but  when  once  well 
started  they  must  be  flooded  or  smothered  out.  In  some  cases  it 
may  be  necessary  to  flood  the  whole  mine,  while  in  others  dams  of  con- 
crete, masonry  or  wood  may  be  built  and  the  spaces  behind  them 
flooded.  In  smothering  a  fire  the  mine  shaft  may  have  to  be  sealed 
up  or  a  portion  of  the  mine  may  be  walled  off  and  sealed  so  tightly 
that  the  fire  dies  out  for  want  of  oxygen.  The  sealing  is  done  by  walls 
of  rock  and  clay,  masonry  or  concrete.  Sometimes  a  wooden  wall  is 
built,  and  clay,  sand  or  other  suitable  material  is  filled  in  behind  it. 
The  waste  or  "  slush  "  from  a  breaker  or  washery  may  in  some  cases 
be  turned  into  the  mine  to  seal  up  the  fire.  It  is  often  extremely 
difficult  to  seal  the  area  so  tightly  that  no  oxygen  can  enter  and 
there  are  some  fires  which  have  burned  for  over  half  a  century 
baffling  all  attempts  to  extinguish  them.  When  sealed  the  area  may 
retain  its  heat  for  years,  and  in  some  mines  the  fire  which  was  sup- 
posed to  be  dead  has  broken  out  as  soon  as  air  was  admitted.  Great 
care  must  therefore  be  exercised  in  reopening  a  sealed  mine  or  local 
area  in  a  mine. 

In  some  cases  fires  have  been  extinguished  by  mining  out  the  seam 
around  the  fire,  thus  isolating  it. 

1  Howell,  S.  P.,  Permissible  explosives  tested  prior  to  Mar.  i,  1915.  U.  S.  Bur.  of 
Mines,  Tech.  Paper  100,  1915. 


CHAPTER  XI 
THE  PREPARATION   AND   USES    OF   COAL 

Introduction 

A  glance  at  the  statistics  of  distribution  of  coal  mined  in  the  United 
States  shows  the  manner  in  which  the  coals  of  various  ranks  are  di- 
vided for  consumption.1  In  1917  the  distribution  of  approximately 
80  million  tons  of  Pennsylvania  anthracite  was  as  follows:  nearly  51 
million  tons  were  of  domestic  sizes;  18  million  tons  of  steam  sizes; 
6  million  tons  were  used  by  railroads  and  over  4  million  tons  exported. 
For  the  same  year  about  366  million  short  tons  of  bituminous  coal, 
mined  and  distributed  in  this  country,  were  divided  as  follows: 

Used  at  mines  for  steam  and  heat 12,117,159  tons 

"  in  manufacture  of  beehive  coke 52,246,612 

"  in  manufacture  of  by-product  coke S^SQS^SQ 

"  in  manufacture  of  coal  gas ........ 4,959,697 

"  by  electrical  utilities 31,692,722 

"  for  domestic  purposes 57,104,000 

"  for  industrial  purposes 176,365,939 

In  addition  to  the  coal  included  in  these  figures  about  153  million  tons 
were  used  by  the  railroads  and  over  10  million  tons  were  loaded  at 
seaports  for  bunker  purposes.  Approximately  23  million  tons  were 
exported. 

For  industrial  purposes  and  for  the  use  of  the  railroads,  the  two 
largest  items  of  consumption,  a  great  variety  of  coals  and  grades  of 
coal  may  be  used.  The  same  holds  true  for  the  electrical  utilities, 
mine  consumption  and  to  a  certain  degree  for  domestic  purposes. 
For  certain  types  of  industrial  operations  where  special  coals  are 
required  as,  for  example,  in  smithing,  there  were  255,000  tons  used. 
For  coking  purposes  certain  limits  may  be  placed  on  the  grade  and 
ranks  of  coal  used,  as  low  sulphur  coals  and  coking  varieties  must  be 
selected. 

For  domestic  purposes  the  distinctions  made  lie  more  in  the  prep- 
aration of  the  coal  for  use  than  in  the  rank  or  grade  of  the  coals,  since 
all  ranks  from  lignite  to  anthracite  are  extensively  used  and  some 
of  the  coals  are  of  very  low  grade.  For  gas  manufacture  particular 
types  of  fairly  high  volatile  coals  are  best. 

1  U.  S.  Geol.  Survey,  Mineral  Resources  of  the  United  States,  1917. 

299 


3oo 


THE  PREPARATION  AND  USES  OF  COAL 


Preparation  of  Coal  for  Domestic  Purposes 

Anthracite.  —  On  account  of  its  high  heating,  low  smoke-producing 
and  long-burning  qualities,  and  its  freedom  from  dirt  and  dust, 
anthracite  has  long  been  a  favorite  domestic  fuel.  The  operation  of 
preparing  it  for  market  has  become  quite  a  highly  developed  me- 
chanic art. 


FIG.  101.  —  Slate  pickers  in  an  anthracite  breaker.     (Photo  by  courtesy  of  R.  P.  Hutch- 
inson  of  the  Bethlehem  Fabricators  Inc.) 

There  are  two  main  objects  in  view  in  breaking  and  separating 
anthracite,  one  being  that  of  getting  it  into  uniform  sizes  so  that  it 
will  readily  burn  in  a  grate  and  the  other  that  of  cleaning  the  coal 
by  washing  out  the  small  particles  of  mineral  matter  and  by  removing 
the  larger  fragments  of  slate  by  hand  or  with  mechanical  separators. 
According  to  Sterling1  the  methods  of  preparation  may  be  grouped 
under  three  classes,  as  follows:  (i)  Dry  preparation,  used  for 
lump  coal  which  comes  from  the  mine  dry  and  which  readily 

1  Sterling,  Paul,  The  preparation  of  anthracite.  Trans.  Amer.  Inst.  Min.  Eng.,  Vol. 
42,  p.  264,  1912.  Also  Peele's  Handbook  for  Mining  Engineers,  p.  1842. 


ANTHRACITE 


301 


separates  from  the  waste  rock;  (2)  Combination  of  dry  and  wet 
preparation  employed  when  the  run-of-mine  contains  a  high  per- 
centage of  impurities,  perhaps  up  to  55  per  cent,  but  also  consid- 
erable lump  coal  which  can  be  handled  as  in  (i);  (3)  Wet  prepara- 
tion, when  the  run-of-mine  is  high  in  impurities  and  is  discolored 
with  iron  or  clay.  This  type  of  coal  occurs  near  the  surface  and  in 
disturbed  zones  in  the  mine. 

The  coal  is  taken  from  the  mine  mouth  to  the  breaker  in  the  mine 
cars  or  by  conveyors,  depending  upon  the  relative  position  of  the  pit 
mouth  and  the  top  of  the  breaker.  It  is  first  passed  over  a  sizing  screen, 
sometimes  known  as  a  bull  shaker,  which  sorts  the  lump  from  the 
smaller  material,  the  former  going  to  a  picking  table  and  the  latter, 
which  is  often  called  the  mud-screen  product,  moving  along  to  be 
treated  by  the  wet  process,  (Fig.  101).  On  the  picking  table  pieces 
of  rock  are  removed  by  hand.  If  coal  and  rock  adhere  the  lumps  are 
removed  to  a  special  table  where  they  are  broken  by  hand  and  the 
rock  sent  to  the  rock  pile. 

The  cleaned  lump  goes  to  a  pocket  for  shipment  as  lump  or  to  the 
rolls  to  be  broken,  depending  upon  the  demand  for  the  different 
sizes.  The  rolls,  which  are  furnished  with  teeth,  break  the  coal  into 
the  sizes  indicated  by  the  following  table: 

TABLE  SHOWING  MARKET  SIZES  FOR  ANTHRACITE  AND 
SCREEN   OPENINGS   IN   INCHES 


Size  of  coal 

Punched  plate 

Woven  wire 

Round 

Square 

Over 

Through 

Over 

Through 

Over 

Through  , 

Lump     

6^ 
4^ 
3* 

*& 

ife 

JP 

f 

A 

X 

'ei 

4^ 

I 

*« 

f 

P 

A 

if 

2 
I* 

« 

A 

£ 

2 

If 

1  3 

16 
9 
T  6 

Ji' 

2 

ti 

3 
4 

A 

i\ 

If' 

2 
if 

1 

Steamboat 

Broken  

Egg.  . 

Stove 

Chestnut 

Pea 

Buckwheat  

Rice  

Barley  

Buckwheat  No.  4  

302 


THE   PREPARATION  AND   USES  OF   COAL 


The  percentages  of  each  size  allowable  in  the  other  sizes  and  the 
percentage  of  slate  and  bone  allowable  in  the  various  sizes  is  shown 
in  the  following  table: 

TABLE  OF  STANDARDS  OF  PREPARATION  IN  PERCENTAGE 


May  contain 

Broken 

Egg 

Stove 

Nut 

Pea 

Buckwheat 

Rice 

Barley 

Of  slate  

I 

2 

2-5 

4 

8 

IO 

15 

IS 

Of  bone  

2 

2 

4 

5 

5 

Of    next     size 

larger  

5 

5 

10 

5 

8 

8 

8 

Of    next     size 

smaller  

2O 

5° 

5° 

15 

ISB 

15 

25 

. 

isR 

After  screening,  the  steamboat  size  is  either  sent  to  a  pocket  and 
shipped  or  sent  to  other  rolls  and  further  crushed,  according  to  the 
condition  of  the  market  for  various  sizes.  This  process  is  continued 
until  the  whole  operation  is  complete  except  that  certain  portions  of 
the  coal  are  put  through  the  wet  process  to  clean  it  if  necessary.  The 
course  followed  is  clearly  outlined  by  Ashmead1  in  the  accompanying 
diagram,  (Fig.  102). 

The  screens  used  in  recent  years  are  largely  of  the  shaker  type 
rather  than  the  oscillating  or  gyratory  screens.  The  advantages  of 
the  shaker  type,  according  to  Sterling,  are:  low  first  cost;  ease  with 
which  it  may  be  repaired  and  maintained;  good  sizing  of  smaller 
sizes;  large  capacity;  ability  to  size  material  not  over  150  pounds 
in  weight  in  going  to  the  picking  room.  The  revolving  screen  does 
not  vibrate  the  breaker  as  much  as  a  shaker  screen  and  it  performs 
exact  screening  and  sizing.  It  has  smaller  capacity,  however,  and 
requires  more  space  than  shaking  screens  of  the  same  capacity.  Only 
about  one-eighth  of  the  surface  is  in  contact  with  the  coal  at  one 
time.  The  first  cost  and  maintenance  are  high. 

There  have  been  some  recent  developments  in  the  use  of  jigs,  es- 
pecially of  the  plunger  type,  for  separating  the  slate  from  the  coal, 
and  mechanical  pickers  are  used  a  great  deal  for  the  same  purpose 
in  dry  preparation.  Where  hand  picking  is  done  the  moving  table 

1  Ashmead,  D.  C.,  Modernized  breaker  with  hand  pickers,  spirals,  jigs  and  concen- 
trators. Coal  Age,  Vol.  18,  p.  585,  1920. 


ANTHRACITE 


303 


3°4 


THE  PREPARATION  AND  USES  OF  COAL 


is  found  to  be  an  advantage.  In  the  automatic  mechanical  pickers 
the  moving  table  is  so  arranged  as  to  give  it  a  pitch  in  two  directions, 
first  transverse  to  the  table,  and  second  along  the  center  line.  This 
requires  the  moving  material  to  travel  up  hill  and  the  coal  is  separ- 
ated from  the  rock,  owing  to  difference  in  specific  gravity  and  friction 


FIG.  103.  —  Cross-section  of  Alliance  Breaker,  showing  loading  method.     (After  Ash- 
mead:  Reproduced  by  courtesy  of  Coal  Age.) 

of  the  coal  and  slate  on  the  table.  The  rock  discharges  at  one  point 
and  the  coal  at  another.  With  the  increased  efficiency  of  the  cleaning 
equipment  in  the  modern  breakers  it  is  now  possible  to  save  a  much 
larger  percentage  of  the  coal  than  formerly  and  some  of  the  culm 
banks  can  be  reworked.  Several  large  Pennsylvania  anthracite 
companies  have  quite  recently  installed  tables  of  the  Deister-Over- 
strom  type  for  washing  the  barley  and  smaller  sizes  of  coal.  There 


BITUMINOUS   COAL 


305 


seems  to  be  a  good  future  in  the  Anthracite  region  for  the  application 
of  some  of  the  devices  so  long  used  for  ores,  and  adopted  in  some  of 
the  western  fields  for  coal  washing  and  separation. 

Bituminous  coal.  —  It  is  becoming  more  and  more  a  custom  to 
wash  and  size  bituminous  and  semibituminous  coal  for  domestic  pur- 
poses. A  cleaner  coal  and  a  coal  which  will  burn  better  and  stand 
storage  better  is  produced  in  this  way,  and  mining  operations  are 
aided  because  some  labor  in  sorting  coal  and  rock  underground  is 
saved.  At  many  mines  simple  bar  screens  are  used  while  at  others 
modern  shaker  screens  have  been  adopted.  The  coal  is  sorted  into 
various  sizes  somewhat  like  anthracite  but  on  a  less  perfectly  devel- 
oped plan.  The  state  of  Illinois  has  probably  been  the  most  advanced 
of  the  states  of  the  Union  in  the  systematic  preparation  of  bituminous 
coal,  and  now  only  about  20  per  cent  of  her  output  is  sold  as  run-of- 
mine,  the  remainder  being  treated  before  shipment  is  made.1  This 
remarkable  development  in  washing  and  sizing  operations  in  Illinois 
is  partly  due,  however,  to  the  fact  that  very  little  of  the  coal  in  the 
state  is  of  coking  quality.  This  is  a  type  which  does  not  need  sizing  for 
market,  although  it  is  customary  to  wash  a  great  deal  of  coking  coal  to 
reduce  the  sulphur  content.  At  mines  where  the  coal  is  only  passed 
over  shaking  screens  and  then  sold,  four  sizes  are  commonly  made; 
these  are  known  by  the  following  names: 


Name 

Size  in  inches 

Per  cent  of  total  output 

Lump 

Over  6 

T  (J 

Eee 

Over  3^  through  6 

TQ 

No.  i  nut       

Over  if  through  3^ 

16 

No.  2  nut  

Over  i    through  if 

II? 

No.  3  nut  

Over    f  through  i 

7 

No.  4  nut  

Over    j  through    f 

7 

No.  5  nut  

Through  j 

21 

The  sizes  for  these  different  types  vary  somewhat  in  different  fields. 
In  some  areas  the  lump  sizes  run  through  8  grades  of  lump,  from  8- 
inch  lump  to  ij-inch  lump  and  on  down  through  chunk,  egg,  nut,  pea 
and  screenings.  At  some  mines  mechanical  pickers,  as  well  as  men 
and  boys,  are  employed  and  some  companies  wash  the  coal  in  addition 

1  Andros,  S.  O.,  Coal  mining  in  Illinois.    Illinois  Coal  Mining  Investigations.    Bull. 
13,  p.  202.    Urbana,  1914. 


3°6 


THE   PREPARATION  AND   USES   OF   COAL 


to  screening  it.  Washing  tends  to  remove  clay,  slate  and  iron  pyrite 
and  this  is  quite  an  advantage  for  high  sulphur  coals  for  coking. 
An  elaborate  washery  was  put  into  operation  at  the  United  States 
Fuel  Company's  mine  at  Benton,  Franklin  County,  Illinois  in  the 
fall  of  1918. l  It  has  been  the  hope  of  mining  men  that  the  greater 
part  of  the  sulphur  could  be  removed  from  coal  by  washing  out  the 
pyrite.  Unfortunately,  as  previously  pointed  out  in  this  text,  it  is 
impossible  to  wash  out  the  sulphur  in  organic  compounds,  or  the 
finely  divided  pyrite  which  is  almost  always  present. 


FIG.  104.  —  The  Loree  Breaker.     (Photo  by  courtesy  of  R.  P. 
Hutchinson,  Bethlehem  Fabricators,  Inc.) 

Storage 

The  storing  of  coal  is  a  very  important  item  in  many  industries. 
If  it  is  not  stored  at  times  when  it  is  plentiful  and  transportation 
facilities  are  good,  plants  may  be  tied  up  owing  to  break-downs  in 
traffic  or  mining  operations,  resulting  from  storms,  strikes  or  other 
causes.  Another  advantage  in  storing  coal  is  that  it  distributes  the 
demand  more  uniformly  over  the  whole  year  and  the  peak  load  does 

1  Campbell,  J.  R.,  Mechanical  separation  of  sulphur  minerals  from  coal.  Trans.  Amer. 
Inst.  Min.  and  Met.  Eng.,  Vol.  LXIII,  p.  683,  1920.  Also,  Frazer,  Thomas  and  Yancey, 
H.  J.,  Some  factors  that  affect  the  washability  of  a  coal,  p.  768. 


SPONTANEOUS   COMBUSTION  307 

not  always  fall  in  the  winter  when  most  coal  is  likely  to  be  needed. 
According  to  Stock  the  coal  should  be  stored  as  near  the  place  where 
it  will  be  used  as  possible,  although  it  is  practical  to  store  at  the  mines 
temporarily  when  the  car  supply  is  short.  The  main  objections  to 
storage  of  coal  in  large  amounts  are  the  breakage,  the  cost  of  re- 
handling,  danger  of  fire  from  spontaneous  combustion  or  other  causes, 
the  deterioration  from  weathering,  the  difficulty  in  securing  adequate 
storage  facilities  in  large  cities  where  the  coal  may  be  stored  near 
the  plant  in  which  it  is  to  be  used,  and  the  possibility  of  a  sudden 
and  considerable  drop  in  price.1 

Spontaneous  combustion.  —  The  cause  of  spontaneous  combustion 
is  heating  of  the  coal  by  oxidation  and  other  agencies.  Oxidation  is 
continually  going  on  in  coal  exposed  to  the  air  and  there  is  a  general 
impression  that  sulphur  in  the  form  of  pyrite  is  responsible  for  much 
of  the  trouble.  This  is  not  the  real  cause  although  it  may  aid  the 
chemical  processes  producing  the  heat.  Sulphuric  acid  is  developed 
to  a  certain  extent  in  the  weathering  of  iron  pyrite  and  since  it  is  such 
a  strong  oxidizing  agent  and  generates  so  much  heat  on  coming  in 
contact  with  water  the  presence  of  pyrite  will  naturally  have  an  effect 
on  chemical  action.  It  should  be  borne  in  mind,  however,  that  the 
condition  in  which  the  pyrite  occurs  in  the  coal,  whether  finely  divided, 
or  coarsely  crystallized,  will  have  some  influence  on  its  rate  of  weather- 
ing and  it  is  found  that  the  rate  varies  greatly.  Specimens  of  pyrite 
in  a  collection  in  a  laboratory  show  great  differences  in  the  rate  of 
alteration.  Some  will  break  down  in  the  course  of  a  few  years  while 
others  will  remain  perfectly  bright  for  an  indefinite  period. 

In  a  recent  paper  some  English  writers2  have  claimed  that  fusain, 
(mother-of-coal  or  mineral  charcoal)  probably  aids  spontaneous  com- 
bustion owing  to  the  ease  with  which  it  crumbles  to  powder  and  takes 
fire.  It  smoulders  in  many  cases  without  any  evidence  of  flame. 
These  writers  have  also  found,  as  previously  mentioned  in  this  work, 
that  mineral  charcoal  contains  a  higher  percentage  of  ash  and  fixed 
carbon  than  the  coal  in  which  it  occurs  and  that  it  is  deleterious  to  the 
production  of  good  coke.  It  seems  possible  to  the  writer,  in  view  of 

1  Norris,  R.  V.,  The  storage  of  anthracite.     Trans.  Amer.  Inst.  Min.  Eng.,  Vol.  XLII, 
p.  314,  1912.     (Full  discussion  of  systems  of  storage  and  handling.) 

2  Sinnatt,  F.  S.,  Stern,  H.,  and  Bayley,  F.,  Does  fusain  cause  mine  and  bin  fires,  spoil 
coke  and  aid  explosions?     Coal  Age.     Vol.  18,  p.  384,  1920. 


308  THE  PREPARATION  AND  USES  OF   COAL 

the  great  absorptive  quality  of  wood  charcoal,  that  mineral  charcoal 
may  have  the  power  of  occluding  within  its  walls  more  gases  than  or- 
dinary coal,  and  the  presence  of  these  gases  would  influence  spon- 
taneous combustion.  This  would  be  a  very  interesting  field  for  in- 
vestigation. 

An  investigation  of  the  causes  of  spontaneous  combustion  with 
special  reference  to  Illinois  coals  was  carried  out  by  Parr  and  Kress- 
mann1  and  their  conclusions  were  that  the  following  factors  entered 
into  a  consideration  of  the  subject:  (i)  kind  of  coal  with  regard  to 
its  volatile  matter;  (2)  purity  of  the  coal;  (3)  presence  of  pyrite  and 
other  sulphur  compounds;  (4)  temperature  of  the  coal;  (5)  size  of 
the  fragments;  (6)  presence  of  occluded  gases;  (7)  presence  of  mois- 
ture; (8)  accessibility  of  oxygen;  (9)  pressure  on  the  coal. 

Regarding  the  kind  of  coal,  it  is  found  that  those  high,  or  fairly  high, 
in  volatile  matter  such  as  lignites,  subbituminous,  bituminous  and 
semibituminous  coal  are  the  only  ones  which  are  likely  to  take  fire. 
The  anthracitic  coals  have  too  high  an  ignition  temperature  and  they 
weather  too  slowly  to  take  fire  readily.  According  to  Fayol  lignite 
as  fine  dust  takes  fire  at  150°  C.,  gas  coal  at  200°  C.,  coke  at  250°  C. 
and  anthracite  at  300°  C.  or  above.  He  also  found  that  coal  absorbed 
oxygen  about  twice  as  fast  as  did  pyrite. 

The  pure  coals  seem  to  oxidize  more  rapidly  than  those  with  more 
foreign  matter.  The  effect  of  pyrite  has  already  been  described  above. 
The  size  of  the  coal  is  an  important  factor  as  fine  coal  is  a  much  more 
rapid  absorbent  of  oxygen  than  lump  and  is  dangerous  in  storage. 

Occluded  gases  of  an  inflammable  type,  such  as  methane,  no  doubt 
favor  spontaneous  combustion,  but  to  what  extent  is  unknown. 

Moisture  under  certain  conditions  aids  the  process  since  it  influ- 
ences the  oxidation  of  pyrite  and  coal.  Accessibility  of  oxygen  is 
without  question  an  important  factor. 

Pressure  is  believed  to  be  an  important  factor  in  aiding  the  devel- 
opment of  heat  in  coal,  but  to  what  extent  and  in  what  manner  is  not 
very  fully  understood. 

Some  of  the  remedies  suggested  for  spontaneous  combustion  are: 
storage  under  water  to  eliminate  oxidation;  exclusion  of  fine  coal  by 
screening,  or  its  regular  distribution  throughout  the  pile;  keeping 

1  Parr,  S.  W.,  and  Kressmann,  F.  W.,  The  spontaneous  combustion  of  coal,  Illinois 
Experiment  Station,  Bull.  46,  1910. 


BRIQUETTING  309 

the  piles  low,  only  a  few  feet  hign;  keeping  the  coal  away  from  ex- 
ternal sources  of  heat  such  as  boilers,  pipes  or  the  sun's  rays;  keeping 
it  dry  unless  completely  submerged;  and  elimination  of  high  sulphur 
coals. 

The  deterioration  of  coal  in  storage.  —  From  the  researches  of 
David  White,  previously  mentioned,  it  is  shown  that  oxygen  in  coal 
is  practically  equivalent  to  ash  in  its  anti-calorific  properties.  The 
oxidation  of  coal  therefore  decreases  its  heating  value.  Regarding 
the  deterioration  in  storage  Parr1  concludes  that  very  little  loss  is 
suffered  if  the  temperature  is  not  allowed  to  rise  above  180°  F.  as  there 
is  no  appreciable  evolution  of  CO2  below  200°  F.  The  loss  per  pound 
in  heat  value  is  due  largely  to  an  increase  in  weight  per  unit  mass  of 
coal  on  account  of  the  absorption  of  oxygen,  and  Parr  claims  that 
the  weathered  coal  gave  just  as  satisfactory  results  in  firing,  if  care 
were  taken  in  controlling  the  fire,  as  the  unweathered  coal.  In  an 
earlier  article  Parr  and  Hamilton2  present  the  following  conclusions, 
in  addition  to  those  previously  set  forth:  Submerged  coal  does  not 
lose  appreciably  in  heat  value  while  outdoor  exposure  results  in  a  loss 
in  heating  value  of  from  2  to  10  per  cent.  In  some  cases  the  losses 
appear  to  be  complete  at  the  end  of  five  months.  From  the  seventh 
to  the  ninth  month  the  loss  is  not  appreciable.  Similar  results  were 
obtained  by  Porter  and  Ovitz3  in  experiments  on  Sheridan,  Wyoming 
coal.  They  found  that  this  coal  lost  3  to  5.5  per  cent  of  its  heating 
value  in  about  three  years  in  storage,  70  to  80  per  cent  of  the  loss  oc- 
curring within  the  first  nine  months.  They  also  found  that  storage 
in  air-tight  bottom  bins  had  a  distinct  advantage  over  covering  the 
surface  of  the  coal.  The  slacking  of  the  coal  is  one  of  the  important 
factors  in  weathering  as  it  tends  to  destroy  its  firing  qualities. 

Briquetting4 

The  process  of  briquetting  coal  has  developed  considerably  in  re- 
cent years.  It  is  applied  to  fuels  which  are  dusty,  such  as  peat,  lig- 

1  Parr,  S.  W.,  Effects  of  storage  upon  the  properties  of  coal.     University  of  Illinois, 
Bull.  No.  39,  Vol.  XIV,  1917. 

2  Parr,  S.  W.,  and  Hamilton,  N.  D.,  The  weathering  of  coal.     University  of  Illinois, 
Bull.  No.  33,  1907. 

3  Porter,  H.  C.,  and  Ovitz,  F.  K.,  Deterioration  in  the  heating  value  of  coal  during 
storage.     U.  S.  Bur.  of  Mines,  Bull.  136,  1917. 

4  Franke,  G.,  A  handbook  of  briquetting.     Translated  by  F.  Lantsberry,  Charles 
Griffin  and  J.  B.  Lippincott,  1917. 


310  THE   PREPARATION  AND  USES  OF   COAL 

nite,  fine  slack,  and  culm.  It  consists  of  compressing  the  powdered 
fuel  into  briquets  or  little  bricks,  using  pitch  as  a  bond  to  hold  the 
particles  together.  The  pressing  is  done  at  rather  high  temperatures. 

In  recent  years  much  material  from  the  culm  banks  of  the  anthra- 
cite region  of  Pennsylvania  has  been  recovered,  washed,  dried,  and 
briquetted.  Many  of  the  old  culm  piles  contain  the  coal  which  is  now 
sold  as  barley  and  buckwheat  sizes.  According  to  Dorrance,1  at  the 
Lehigh  Coal  and  Navigation  Company's  plant  the  culm  is  loaded  into 
gondolas  of  ioo,ooo-pound  capacity  and  taken  to  a  track  hopper  at 
the  briquetting  plant.  It  is  elevated  to  the  drying  plant  and  passed 
through  Vulcan  rotary  kiln  driers  which  are  heated  by  gases  from  the 
furnace.  It  is  screened  on  vibrating  screens  of  Newago  type,  the 
material  passing  through  the  finest  screen  going  to  the  refuse  conveyor. 
The  refuse  from  this  and  later  screenings  is  sent  to  the  mines  at  Sum- 
mit Hill  for  slushing  the  mine  fire  burning  there.  Commercially- 
sized  coal  separated  is  sent  to  the  drier  building  for  feeding  the  fur- 
naces. The  material  from  the  screens  is  sent  to  Damon  air  separators 
and  the  coal  retained  from  them  is  sent  to  the  bins  and  from  there  to 
the  mixing-house.  Solid  coal-tar  pitch  is  used  as  a  binder  and  it  is 
fed  into  rolls  and  cracked  to  "  pea  "  and  "  dust"  sizes.  This  is  then 
elevated  to  the  pitch-measuring  apparatus  which  feeds  the  right  pro- 
portion of  pitch  to  a  squirrel-cage  pulverizer  which  in  turn  feeds  it 
into  a  screw  conveyor  with  a  measured  amount  of  culm  material. 
These  materials  then  pass  to  the  briquetting-house  and  are  sent 
through  the  mixers  to  the  presses.  In  the  mixers  the  material  is 
heated  with  superheated  steam  to  about  400°  then  cooled  by  a  cooling 
fan  and  pressed  into  briquets.  Briquets  are  used  by  the  railroads  and 
industrial  concerns,  while  the  little  balls  known  as  boulets  are  sold 
for  domestic  use  since  the  larger  size  does  not  seem  to  burn  as  well 
in  domestic  heaters  as  the  smaller  balls. 

Experiments  have  shown  that  a  great  number  of  binders  may  be 
used  for  briquetting,  but  some  of  them  cost  a  prohibitive  sum.2  The 
nearness  to  the  source  of  supply  influences  to  quite  a  large  extent 
the  choice  of  the  type  of  binder.  The  following  binders  have  proven 
satisfactory  and  they  are  available  in  many  localities:  (i)  Asphalt, 

1  Dorrance,  Charles,  Jr.,  Anthracite  culm  briquets.     Trans.  Amer.  Inst.  Min.  Eng., 
Vol.  XLII,  p.  365,  1912. 

2  Mills,  James  E.,  Binders  for  coal  briquets.    U.  S.  Bur.  of  Mines,  Bull.  No.  24,  1911. 


PRODUCER   GAS 

the  heavy  residuum  from  petroleum,  costing  about  45  to  60  cents  per 
ton  of  briquets  and  used  in  proportion  of  4  in  100.  (2)  Water-gas 
tar  pitch  costing  50  to  60  cents;  5  or  6  per  cent  is  used.  (3)  Coal- 
tar  pitch;  6.5  to  8  per  cent  is  used  per  ton  and  the  cost  per  ton  of 
briquets  runs  65  to  90  cents  for  binder.  Other  substances  which 
might  be  used  are  starch,  sulphite  and  magnesia. 

The  results  of  the  tests  made  on  briquets  by  the  Bureau  of  Mines1 
indicate  that  there  is  considerable  difficulty  in  burning  them  in  do- 
mestic heaters  where  low  temperatures  prevail  so  much  of  the  time, 
as  the  binder  either  tends  to  produce  a  deposit  on  the  interior  walls 
of  the  furnace  and  the  pipes  which  clogs  them,  or  it  burns  off  too 
rapidly  when  the  temperature  rises  quickly.  The  briquets  ignite 
readily  unless  an  inorganic  binder  is  used  or  there  is  too  much  im- 
purity in  the  slack  from  which  they  are  made,  and  they  produce  a 
large  amount  of  smoke  if  not  properly  fired.  Their  relative  efficiency 
is  high,  they  are  clean  and  they  weather  very  well.  It  is  concluded, 
however,  that  there  is  no  justification  for  briquetting  lump  coal 
and  the  main  advantage  in  the  process  lies  in  consolidating  coal  which 
is  in  too  fine  a  condition  or  is  dusty.  Lignite  and  fine  coal,  which 
does  not  coke  may  be  profitably  briquetted  in  many  cases.  Coking 
coals  are  more  easily  handled  without  briquetting  than  non-coking 
types  since  they  are  not  readily  lost  by  running  through  the  grates. 
The  average  cost  of  briquetting  a  ton  of  fuel  has  been  placed  at  about 
$1.00  to  $1.80.  Recent  developments  in  the  briquetting  of  partially 
devolatilized  coal,  or  carbo-coal,  indicate  that  there  is  probably  a  more 
promising  future  along  that  line  than  in  the  briquetting  of  the  raw 
fuel. 

Coals  Used  in  Gas  Manufacture 

Producer  gas.  —  Coals  which  are  used  in  gas  manufacture  may 
vary  greatly  in  quality  and  it  is  difficult  to  fix  limits  as  to  their  prop- 
erties. Fuels  from  peat  to  anthracite  have  been  used  for  the  manu- 
facture of  producer  gas,  which  is  coal  gas  diluted  with  air  and  often 
mixed  with  water-gas.  They  should,  however,  be  comparatively  low 
in  sulphur  and  ash  and  the  fusibility  of  the  ash  is  an  important  fac- 
tor. It  should  not  be  low.  The  size  of  the  coal  also  has  an  impor- 

1  Wright,  C.  L.,  Fuel  briquetting  investigations.    U.  S.  Bur.  of  Mines,  Bull.  58,  p.  191, 


312  THE  PREPARATION  AND  USES  OF  COAL 

tant  bearing  as  coarse  run-of-mine  is  not  good  material.  Egg  and  nut 
sizes  are  desirable  and  screenings  may  be  used.1 

Illuminating  gas.  —  For  illuminating  gas  a  coal  must  be  high  in 
volatile  matter  so  as  to  yield  per  short  ton  at  least  10,000  cubic  feet 
of  gas  at  60°  F.  and  30  inches  mercury  pressure,  and  the  gas  should 
test  1 6  to  1 8  standard  candle  power.  Cannel  coal  has  long  been 
recognized  as  probably  the  most  desirable  coal  for  this  purpose. 
The  quality  of  the  volatile  constituents  is  important  as  well  as  the 
quantity.  The  coal  should  also  yield  a  good  proportion  of  coke. 
The  sulphur  must  be  low,  not  above  ij  and  preferably  below  i  per 
cent,  although  coals  have  been  used  in  some  cases  which  run  up  to 
about  2  per  cent.  The  sulphur  unites  with  hydrogen  to  produce 
hydrogen  sulphide  H2S  and  with  carbon  to  produce  carbon  disul- 
phide  (082).  The  former  is  an  evil-smelling,  poisonous  gas  and  the 
latter  under  certain  conditions  has  a  horrible  odor.  Both  of  these 
gases  burn  to  sulphur  dioxide  (802)  and  this  gas  is  not  only  suffo- 
cating and  objectionable  to  man  but  it  aids  in  tarnishing  metal  house- 
furnishings.  The  sulphur  gases  can  be  removed  from  the  illumin- 
ating gas  at  a  rather  high  and  in  many  cases  prohibitive  cost.2 

The  following  figures  indicate  the  general  chemical  composition  of 
coals  which  have  been  used  and  are  well  adapted  for  gas  making : 

Cannel  Bituminous  gas  coal 

Moisture i .  30-  4 . 50  per  cent  i .  oo-  4 .  oo  per  cent 

Volatile  matter 30.00-39.00  "  28.00-37.00       " 

Fixed  carbon 50.00-60.00  "  54.00-61.00       " 

Ash 2.20-6.00  "  3.50-10.00       " 

Sulphur 0.50-1.05  "  0.80-1.32       " 

B.t.u 13,000-14,500  13,200-14,600 

Water  gas.  —  Water  gas  is  a  commercial  gas  consisting  very  largely 
of  carbon  monoxide  and  hydrogen  and  it  is  made  by  dissociating 
steam  into  hydrogen  and  oxygen,  thus  permitting  the  latter  to  unite 
with  carbon  to  form  carbon  monoxide  (CO).  Anthracite  and  coke 
have  been  most  generally  used  for  this  purpose  but  non-coking  bitu- 
minous coals  might  also  be  used. 

1  Brooks,  G.  S.,  and  Nitchie,  C.  C.,  Gas  producer  practice  in  western  zinc  plants. 
Trans.  Amer.  Inst.  Min.  and  Met.  Eng.,  Vol.  LXIII,  p.  846,  1920. 

2  Odell,  W.  W.,  and  Dunkley,  W.  A.,  Removal  of  sulphur  from  illuminating  gas. 
Trans.  Amer.  Inst.  Min.  and  Met.  Eng.,  Vol.  LIII,  p.  660,  1920. 


POWDERED  FUEL  313 

Smithing  Coals 

No  very  definite  limits  have  been  fixed  for  the  quality  of  smithing 
coals.  Semibituminous  or  "  smokeless  "  coals  have  been  generally 
used  although  anthracite  and  semianthracite  coal  have  also  been 
used.  Some  of  the  requirements  for  a  first-class  coal  of  this  type  are 
low  sulphur,  less  than  i  per  cent;  high  calorific  value;  low  ash;  and 
sufficient  coking  quality  to  seal  over  and  retain  the  fire  when  articles 
are  not  being  inserted  or  withdrawn. 

Coals  for  Cement  and  Tile  Burning 

For  a  cement-burning  coal  the  requirements  are  a  high  calorific 
value,  12,000  B.t.u.  and  upward,  and  a  high  volatile  content.  For 
burning  brick  and  pottery,  coals  of  high  volatile  content  and  non- 
coking  qualities  are  desirable. 

For  burning  porcelain  and  the  finer  grades  of  ceramic  materials 
low  sulphur  is  essential  and  low  ash  desirable.  According  to  Par- 
melee1  the  English  pottery  practice  requires  a  coal  which  comes  near 
the  following  figures:  Total  sulphur,  1.20  per  cent;  sulphur  in  ash 
o.i i  per  cent;  and  volatile  sulphur  1.09  per  cent.  The  practice  in 
America  is  about  as  follows: 

For  Sanitary  ware:  Maximum  i.o  per  cent;  0.5  per  cent  desirable. 

For  Sewer  pipe:  As  high  as  3.10  per  cent  has  been  used  but  1.2  per 
cent  should  be  the  maximum  and  i.i  per  cent  is  about  present  run. 

Terra  Cotta:  i.o  per  cent  is  approximate  and  0.5  per  cent  is  basis 
of  contract. 

Pottery:  i.o  per  cent  contract  basis  and  1.5  per  cent  probable 
content. 

Enameled  brick:  1.3  per  cent  maximum. 

Powdered  Fuel 

Powdered  fuel  must  be  ground  exceedingly  fine  and  then  be  blown 
into  the  furnaces  with  a  supply  of  air  adequate  to  completely  con- 
sume it.  For  ordinary  steam  purposes  the  sulphur  and  a  reasonable 
amount  of  ash  do  not  greatly  affect  the  qualifications,  but  for  use  in 
the  steel  plants  the  sulphur  and  ash  must  be  low.  The  same  rules 
should  govern  the  proportions  of  sulphur  in  such  fuel  as  in  coke.  The 

1  Parmelee,  C.  W.,  Effect  of  sulphur  in  coal  used  in  ceramic  industries.  Trans.  Amer. 
Inst.  Min.  and  Met.  Engv  Vol.  LXIII,  p.  727,  1920. 


314  THE   PREPARATION  AND   USES   OF   COAL 

volatile  matter  should  be  over  30  per  cent  and  the  greater  the  pro- 
portion of  combustible  gas  in  the  volatile  matter  the  better  the  quality, 
other  things  being  equal. 

There  is  an  interesting  new  development  in  the  use  of  coal  as  a 
colloidal  fuel.1  The  use  of  this  type  of  fuel  is  largely  in  the  experi- 
mental stage  but  there  may  be  a  large  future  for  it.  The  colloidal 
fuel  in  which  coal  has  been  concerned  is  very  finely  powdered  coal 
suspended  in  fuel  oil.  Several  types  of  coal  have  been  used  and  the 
calorific  power  developed  has  been  high.  There  seems  to  be  a  pos- 
sibility of  not  only  suspending  the  fine  coal  in  the  liquid  as  a  mechani- 
cal mixture  but  also  of  dissolving  certain  parts  of  it  so  that  it  actually 
goes  into  a  liquid  condition. 

Steam  Coals 

Coals  used  in  the  production  of  steam  include  especially  those 
used  on  ships,  in  locomotives  and  under  stationary  boilers  and  they 
embrace  a  wide  range  in  ranks  and  grades.  The  ideal  steaming  coal 
is  one  combining  high  calorific  power  with  small  smoke-  and  clinker- 
producing,  as  well  as  fairly  long-burning  qualities.  It  should  also  be 
sufficiently  high  in  volatile  matter  to  permit  a  rapid  response  to 
stimulated  firing,  as  a  fireman  on  a  locomotive,  for  example,  may 
need  a  fire  which  responds  rather  quickly  when  heavy  grades  are 
approached.  The  coal  must  also  be  capable  of  standing  storage, 
especially  when  employed  for  bunkering  purposes.  The  presence 
of  sulphur  will  influence  its  qualities  for  storing  as  well  as  the  clink- 
ering  of  the  ash  since  sulphur,  especially  in  the  form  of  mineral  sul- 
phides, seems  to  show  a  marked  influence  in  lowering  the  temperature 
of  fusion  of  the  ash  if  present  in  quantities  over  about  2  per  cent. 
The  character  of  the  ash  and  the  methods  of  firing  will  also  influence 
the  results  to  a  marked  degree.  The  iron  of  the  pyrite  unites  with 
other  elements  and  produces  more  fusible  compounds.  The  sulphur 
compounds  also  break  up  and  form  new  compounds  some  of  which 
corrode  the  furnaces. 

Semibituminous,  or  so-called  "  smokeless,"  coal  has  long  been  rec- 
ognized in  America  and  abroad  as  the  finest  type  of  steam  coal. 

1  Sheppard,  S.  E.,  Colloidal  fuels,  their  preparation  and  properties.  Jour,  of  Ind. 
and  Eng.  Chem.  Vol.  13,  p.  37,  1921. 


COKE 


It  has  the  highest  calorific  value  of  any  coal  and  it  contains  sufficient 
volatile  matter  to  make  it  ignite  a  little  more  readily  than  anthracite. 

Some  of  the  best  steam  coals  in  America  are  the  semibituminous 
coals  of  Virginia,  West  Virginia,  Maryland,  Central  Pennsylvania, 
Arkansas,  and  Alberta,  Canada.  The  steam  coals  of  South  Wales 
have  long  been  famous. 

Analyses  showing  the  limits  in  composition  of  some  of  the  well- 
known  types  of  semibituminous  coals  in  the  United  States  are  as 
follows  i1 


Arkansas 

Maryland 

Pennsylvania 

West  Virginia 

Moisture  
Volatile  matter 
Fixed  carbon.  .  .  . 
Ash 

0.85-  3.50 
II  .40-16.60 
72.00-77.00 
7   4O—I2   OO 

0.38-  3.40 
15.40-27.00 
57.20-76.60 
4  20—  18  so 

0.57-  4.50 
15  .80-27.20 
64.30-78.00 
2   40—12    2O 

0.30-  3.40 
13  .IO-22.OO 
71.90-79.00 
2    OO—  I  I    2O 

Sulphur  
B.t.u  

1.30-   2.8o 
13,200—14,650 

0.80-  4.70 

12,760—14,900 

0.50-    2.IO 
1  3,400—  IA,  6  SO 

0.50-    2.50 
14.  OOO—  14.  Q2O 

An  analysis  of  high-grade  Pocahontas  coal  would  be  illustrated  by 
the  following  figures:  Moisture,  1.31;  Volatile  matter,  16.30;  Fixed 
carbon,  77.06;  Ash,  5.33;  Sulphur,  0.67;  and  B.t.u.  14,746. 

Coking 

The  coking  of  coals  for  the  purpose  of  securing  metallurgical  coke 
is  a  process  which  has  long  been  in  vogue  and  it  has  attained  a  place 
of  great  importance  in  our  industrial  operations.  There  are,  however, 
some  new  phases  of  this  process  which  bid  fair  to  become  of  much 
more  widespread  interest  than  that  of  simply  securing  metallurgical 
coke.  They  are  the  saving  of  the  volatile  products  from  the  coal  and 
the  production  of  solid  fuels  which  will  be  better  suited  than  coal  for 
domestic  use  and  for  some  industrial  purposes. 

Coke.  —  Coke  is  the  hard  residue  obtained  from  heating  coals  in 
the  absence  of  air.  It  has  a  dull  to  submetallic  luster,  is  dark 
gray  to  silvery  gray  in  color  and  is  very  porous,  or  vesicular.  There 
is  sometimes  a  great  variation  in  the  strength  of  coke  made  from  the 
same  coal  seam.  Some  of  it  will  support  the  largest  blast  furnace 

1  Analyses  from  the  Coal  Catalog,  Zern,  E.  N.,  Editor,  Keystone  Publishing  Co., 
Pittsburgh,  1918.  This  work  contains  analyses  of  practically  all  coal  seams  in  the 
country. 


3i6  THE  PREPARATION  AND  USES  OF   COAL 

charges  while  other  portions  will  not.  The  percentage  of  coke  which 
may  be  derived  from  coal  varies  from  about  50  to  80  per  cent,  but  a 
profitable  coking  coal  should  yield  on  the  average  at  least  from  65 
to  70  per  cent  coke. 

Coking  coals.  —  The  question  of  what  physical  and  chemical 
properties  determine  the  quality  of  a  coking  or  caking  coal  has  not 
been  fully  decided.  It  is  known  that  certain  portions  of  a  coking 
coal  are  soluble  in  such  solvents  as  aniline,  phenol,  or  pyridine,  and 
that  these  soluble  constituents  constitute  the  better  coking  ingredients. 
As  previously  stated  in  the  discussion  on  coking  coal  it  has  been 
found  by  Pishel  that  coking  coals  tend  to  adhere  to  the  sides  of  an 
agate  mortar  when  rubbed  with  a  pestle  while  non-coking  coals  do  not. 
White  also  shows  that  there  is  some  relation  between  the  oxygen  and 

TT 

hydrogen  ratio  and  the  coking  quality.     When  —  >  58   the  coal 

TT  TT 

generally  cokes;  when  —  >  55  <  58  the  coal  may  coke;  when  --  > 

5°  <  55  the  coal  is  not  likely  to  coke  satisfactorily.  Exceptions 
must  be  made  for  weathered  coals.  A  test  which  is  often  used,  es- 
pecially in  Europe,  to  determine  the  coking  qualities  of  a  coal  con- 
sists in  mixing  the  powdered  coal  with  sand  and  heating  the  mixture. 
The  coking  quality  is  judged  from  the  ability  of  the  coal  to  cause  the 
§and  grains  to  stick  together  in  a  coherent  mass,  and  the  greater  the 
amount  of  sand  the  coal  can  cement  the  better  its  coking  qualities. 
The  relative  qualities  of  the  various  coals  are  fixed  by  a  scale  made 
for  that  purpose.  All  coals  leave  a  residue  but  in  many  cases  it  is 
powdery  and  incoherent  and  of  no  value  unless  it  is  briquetted.  It 
is  assumed  that  a  good  coking  coal  should  run  over  30  per  cent  vola- 
tile matter  and  have  not  more  than  i  J  per  cent  sulphur  and  0.02  per 
cent  phosphorous. 

The  requirements  of  the  American  Society  for  Testing  Materials, 
for  standard  foundry  coke  are  that  the  dry  coke  shall  not  exceed  the 
following  limits  in  chemical  composition : 

Volatile  matter not  over      2 .  o  per  cent 

Fixed  carbon not  under  86.0       " 

Ash not  over    12.0       " 

Sulphur not  over      i .  o       " 

Sulphur  in  coke.  —  Owing  to  the  fact  that  the  mineral  constit- 
uents in  the  coal  mostly  enter  the  coke  with  the  ash  some  of  the  sulphur 


SULPHUR  IN  COKE  317 

is  carried  into  the  coke.  The  statement  is  frequently  made  that 
approximately  one-half  of  the  sulphur  of  the  coal  is  driven  off  and  the 
other  half  remains  in  the  coke.  This  assumption  has  been  largely 
verified  by  the  recent  work  of  Powell1  although  some  factors  not  always 
considered  must  be  taken  into  consideration  in  dealing  with  this 
subject.  Sulphur  in  the  coal  may  be  in  three  forms:  mineral  sul- 
phides, as  pyrite  and  related  minerals;  organic  sulphur,  in  some  un- 
determined form;  and  sulphates,  in  small  amounts.  The  organic 
type  occurs  in  quantities  ranging  from  0.5  to  2.0  per  cent  and  the 
quantity  is  nearly  uniform  for  a  seam  or  locality.  Apparently  this 
uniformity  is  due  to  the  nature  of  the  plants  which  grew  in  that 
locality  and  to  the  bacteriological  and  other  conditions  existing  at 
that  time.  Pure  pyrite  is  completely  decomposed  at  1000°  C.  and 
the  resulting  products  are  ferrous  sulphide  and  free  sulphur,  the 
latter  uniting  with  hydrogen  if  this  element  be  available  to  form  hydro- 
gen sulphide.  A  negligible  amount  of  the  sulphur  remains  in  the 
ferrous  sulphide  in  the  form  of  a  solid  solution  known  as  pyrrhotite, 
or  magnetic  sulphide  of  iron.  The  sulphur  is  thus  practically  equally 
divided  between  the  volatile  and  residual  constituents.  From  his 
tests  on  the  carbonization  of  coals  Powell  concludes  as  follows:  (i) 
At  300°  C.  decomposition  of  the  pyrite  begins  with  the  formation  of 
pyrrhotite  and  hydrogen  sulphide.  The  reaction  is  complete  at  600°  C. 
and  reaches  its  maximum  between  400  and  500°  C.  (2)  At  600°  C. 
the  reduction  of  sulphates  to  sulphides  is  complete.  (3)  Decomposi- 
tion of  J  to  J  of  the  organic  sulphur  takes  place  to  form  hydrogen 
sulphide.  Most  of  this  reaction  occurs  below  500°  C.  (4)  A  small 
part  of  the  organic  sulphur  decomposes  to  form  volatile,  organic 
sulphur  compounds  most  of  which  enter  the  tar.  This  reaction  takes 
place  chiefly  at  the  lower  temperatures  of  the  process.  (5)  A  portion 
of  the  pyrrhotite  disappears  and  the  sulphur  apparently  enters  into 
combination  with  carbon.  This  reaction  is  most  active  at  500°  or 
more.  Between  400  and  500°  C.  the  organic  sulphur  not  accounted 
for  above  undergoes  decided  changes  and  ceases  to  resemble  the 
original  sulphur  in  the  coal.  It  appears  therefore  that  the  percentage 
of  sulphur  originally  in  the  coal  rather  than  the  form  of  the  sulphur 
will  be  the  prevailing  factor  to  be  considered.  Some  carbon  bisul- 

1  Powell,  A.  R.,  Some  factors  affecting  the  sulphur  content  of  coke  and  gas  in  the 
carbonization  of  coal.    Jour.  Ind.  and  Eng.  Chem.  Vol.  13,  p.  33,  1921. 


3l8  THE  PREPARATION  AND   USES  OF   COAL 

phide  is  formed  from  hydrogen  sulphide  where  it  passes  over  red-hot 
coke.  If  hydrogen  is  passed  through  coke  at  a  temperature  above 
600°  C.  a  marked  evolution  of  hydrogen  sulphide  occurs  although  the 
coke  had  ceased  to  evolve  hydrogen  sulphide  at  about  600°  C.  The 
effect  of  the  hydrogen  is  to  aid  the  decomposition  of  iron  pyrite  at  a 
temperature  below  500°  C.  and  the  decomposition  of  organic  sulphur 
compounds  at  temperatures  above  500°  C.  Hydrogen  over  a  coke 
containing  1.2  per  cent  sulphur  was  saturated,  when  it  contained 
about  0.25  pounds  of  sulphur  per  1000  cubic  feet  with  the  coke  at 
900°  C.  Hydrogen  can  therefore  scarcely  be  regarded  as  an  agent 
which  could  be  profitably  employed  to  remove  sulphur  from  coke. 

Apparently  the  gases  given  off  in  the  coking  process  play  an  active 
part  in  removing  the  sulphur  from  the  coke  if  they  can  be  relieved  of 
their  load  of  sulphur  and  returned  over  the  coke.  Less  sulphur  was 
found  in  the  by-product  coke  when  the  gases  were  returned  in  contact 
with  the  coking  mass  than  in  the  coke  where  the  gases  were  drawn 
entirely  away  from  the  mass.  One  may  predict  therefore,  that  some 
method  may  be  devised  to  eliminate  to  quite  an  extent  the  sulphur  in 
the  coke. 

Beehive  coking.  —  The  earliest  forms  of  beehive  ovens,  which 
get  their  names  from  their  shape,  were  built  of  clay  but  the  modern 
ovens  are  standardized  in  size  and  form  and  are  constructed  of  mas- 
onry, brick  and  tile.  Fire  brick  is  used  for  lining  and  the  space  between 
the  lining  and  outside  walls  is  filled  with  waste  brick  and  other  ma- 
terial to  prevent,  as  far  as  possible,  the  loss  of  heat  to  the  exterior. 
The  ovens,  which  are  usually  12.5  feet  long  by  about  7  feet  high 
internally,  are  arranged  in  a  double  row  and  connected  with  a  com- 
mon flue,  the  opening  to  which  is  controlled  by  a  damper.  In  some 
places  the  hot  waste  gases  are  used  for  producing  steam  in  the  power 
plant  or  for  heating  purposes.  The  cost  of  an  individual  oven  in  nor- 
mal times  runs  from  about  $450 .  oo  to  $500 .  oo. 

The  oven  is  started  at  first  with  a  wood  fire  and  coal  is  added  grad- 
ually for  from  two  to  four  days  to  prevent  cracking  the  brickwork. 
A  small  charge  may  then  be  added  and  the  front  door  bricked  up, 
leaving  holes  for  air.  The  burning  of  this  charge,  which  does  not 
give  good  coke,  is  performed  to  heat  the  oven  and  the  resulting  ma- 
terial may  be  rejected  or  used  to  heat  other  ovens.  When  the  oven 
is  hot  a  charge  is  loaded  in  after  the  front  door  has  been  bricked  up 


BEEHIVE   COKING 


319 


about  two- thirds  of  the  distance  to  the  top.  The  charge  for  a  stand- 
ard oven  is  about  5  tons.  The  proportionate  swelling  of  the  coal  on 
heating  varies  with  different  coals. 

In  many  places  the  coal  is  crushed  to  about  \  mesh  before  charging, 
unless  it  be  finely  divided  when  it  comes  from  the  mine.  The  charge 
is  carefully  leveled  with  a  leveling  bar  and  the  door  bricked  and 


FIG.  105.  —  Beehive  ovens  at  the  Isabella  plant  of  the  Hecla  Coal  and  Coke  Co. 
courtesy  of  the  Hillman  Coal  and  Coke  Company,  Pittsburgh,  Pa.) 


(By 


sealed  up  within  about  ij  inches  of  the  top,  or  far  enough  to  admit 
just  about  the  right  amount  of  air  to  burn  the  gas  above  the  charge. 
During  the  latter  part  of  the  process  the  oven  is  sealed  tightly  to 
prevent  entrance  of  air,  which  causes  loss  of  coke  by  combustion. 
The  length  of  time  the  coke  is  burned  depends  upon  the  purpose  to 
which  it  is  to  be  put.  The  best  foundry  coke  is  burned  for  about 
seventy  hours  but  about  forty-five  hours  is  the  time  many  ovens  are 
run  for  other  types  of  coke. 


320  THE   PREPARATION  AND   USES   OF   COAL 

When  the  charge  is  burned  the  "  coke-puller  "  places  a  sort  of 
iron  sprinkler  with  comparatively  large  orifices,  in  the  oven  and 
quenches  the  coke,  applying  upwards  of  1000  gallons  of  water  to  each 
oven.  Care  should  be  exercised  so  that  the  lower  part  of  the  oven 
will  not  be  so  cooled  with  excess  water  that  it  will  not  start  the  fresh 
charge  when  it  is  added.  The  coke  is  then  drawn  either  by  hand  or 
with  a  drawing  machine  and  is  loaded  with  a  fork  so  that  the  fines 
are  separated. 

The  Coppee  type  of  oven.  —  In  an  effort  to  exclude  all  direct  access 
of  air  to  the  coking  chamber  Coppee  introduced  a  retort  type  of  oven 
in  1 86 1.1  The  oven  consists  of  narrow  rectangular  chambers  about 
30  feet  long  and  3^  feet  high.  They  are  built  with  a  slight  taper 
towards  one  end  to  lessen  the  friction  of  discharging.  The  ovens 
are  charged  at  the  top  and  the  gases  pass  into  a  series  of  vertical  flues 
into  which  enough  air  is  admitted  to  permit  the  combustion  of  the 
gases.  The  hot  gases  move  downwards  into  a  sole  flue  and  after 
passing  under  the  whole  length  of  the  oven  they  return  to  a  chimney 
by  the  sole  flue  of  the  adjoining  oven.  They  pass  over  boilers  to 
utilize  the  heat  and  then  up  a  chimney.  The  oven  is  discharged  by 
a  pusher  and  the  coke  is  quenched  outside  the  oven.  The  advan- 
tages claimed  for  this  type  over  the  ordinary  beehive  oven  are:  greater 
yield  because  of  exclusion  of  air  from  the  coking  chamber;  shorter 
coking  period,  because  hot  gases  are  utilized;  saving  in  oven  heat, 
because  of  external  quenching  and  use  of  mechanical  appliances. 

By-product  coking.  —  The  beehive  oven  has  long  been  recognized 
as  an  extremely  wasteful  apparatus  and  the  time  is  rapidly  coming 
when  it  will  be  entirely  superseded  by  the  by-product  type  which  will 
save  all  of  the  volatile  constituents  as  well  as  the  coke.  It  was  thought 
for  a  long  time  by  metallurgists  that  the  coke  made  in  by-product 
ovens  was  inferior  to  that  made  in  beehive  ovens,  but  the  by-product 
coke  has  become  quite  popular  and  it  has  been  found  that  in  regular 
operation  the  consumption  of  by-product  coke  per  ton  of  pig  iron 
manufactured  is  from  100  to  300  pounds  less  than  of  beehive  coke, 
in  the  same  operation.2  Further,  the  energy  used  in  coking  a  ton  of 

1  Byrom,  T.  H.,  and  Christopher,  J.  E.,  Modern  coking  practice.     Crosby,  Lockwood 
and  Son,  1910. 

2  Sperr,  F.  W.  Jr.,  and  Bird,  E.  H    Bv-product  coking.    Jour.  Ind.  and  Eng.  Chem., 
Vol.  13,  p.  26,  1921. 


BY-PRODUCT  COKING 


321 


coal  in  a  beehive  oven  is  9,388,000  B.t.u.,  the  equivalent  of  671 
pounds  of  coal,  or  33.5  per  cent  of  the  heating  value  of  the  coal,  while 
in  the  same  operation  in  a  by-product  oven  the  energy  expended  is 
2,408,000  B.t.u.,  the  equivalent  of  172  pounds  of  coal,  or  8.6  per  cent 
of  the  heating  value  of  the  coal. 

As  pointed  out  above  it  is  apparent  that  it  is  possible  to  produce 
lower  sulphur  coke  from  a  given  coal  in  the  by-product  than  in  the 
beehive  oven.  Coals  running  as  high  as  35  per  cent  volatile  matter 
have  been  used  in  a  by-product  oven  although  it  is  customary  to  mix 
high  volatile  coals  with  lower  volatile  types  and  thus  produce  a  suit- 
able mixture.  Kreisinger  gives  the  following  figures  as  representa- 


FIG.  1 06.  —  Semet-Solvay  coke  pusher  and  cross-section  of  a  regenerative 
oven.     (By  courtesy  of  the  Semet-Solvay  Co.) 

tive  of  the  composition  of  the  coal  from  a  number  of  mines  used  in 
making  by-product  coke:  Moisture,  2.77  per  cent;  Volatile  matter, 
34.17;  Fixed  carbon,  56.94;  Ash,  8.99;  and  Sulphur,  1.37.  The  an- 
alysis of  the  coke  runs:  Moisture,  0.79  per  cent;  Volatile  matter, 
2.80;  Fixed  carbon,  79.29;  and  Ash,  17.14.  In  general,  coals  used 
run  from  26  to  35  per  cent  volatile  matter.  The  sulphur  must  not 
exceed  i  per  cent  in  first-grade  coke,  and  the  ash  in  the  coal  must  be 
less  than  8  per  cent  if  used  for  manufacture  of  first-grade  coke.  For 
second-grade  coke  sulphur  has  been  placed  at  1.20  per  cent  as  a  maxi- 
mum and  ash  in  the  coal  at  10  per  cent. 

In  1893  the  production  of  beehive  coke  in  the  United  States  was 
9,464,730  short  tons  and  of  by-product  coke  12,850  tons.  In  1919 
the  production  of  beehive  coke  was  19,650,000  short  tons  and  of 
by-product  25,171,000  tons,1  showing  that  the  supremacy  of  the 

1  Mineral  Industry,  p.  116,  1919. 


322 


THE  PREPARATION  AND   USES  OF   COAL 


beehive  is  rapidly  waning.  The  by-products  recovered  for  the  year 
1919  amounted  to  668,200,000  pounds  ammonium  sulphate  or  its 
equivalent;  251,000,000  gallons  of  tar;  84,800,000  gallons  of  crude 
light  oil  and  367,700,000,000  cubic  feet  of  gas. 

The  cost  of  installing  a  large  by-product  plant  has  been  one  of  the 
obstacles  in  the  way  of  a  more  rapid  introduction  of  the  ovens  although 
they  are  becoming  very  numerous,  many  of  them  being  established 


FIG.  107.  —  Semet-Solvay  plant  constructed  for  the  Chattanooga  Coke  and 
Gas  Co.     (By  courtesy  of  the  Semet-Solvay  Co.) 

in  connection  with  the  large  metallurgical  plants  where  the  gas  and 
tar  are  utilized  for  fuel.  They  are  also  built  near  cities  where  the  gas 
can  be  utilized.  The  cost  of  some  of  the  large  plants  runs  from 
several  hundred  thousand  to  several  million  dollars. 

The  main  principle  of  the  by-product  oven  is  the  heating  of  a 
chamber  full  of  coal,  which  is  connected  with  a  system  of  condensers 
and  stills.  It  is  distinctly  a  distillation  process.  There  are  several 
types  of  ovens,  such  as  the  Semet-Solvay,  Koppers,  Otto-Hoffman, 
Otto-Hilgenstock,  Coppee,  Roberts,  Willputte  and  Klonne.  Of  these 
the  Semet-Solvay  and  Koppers  are  the  most  common  in  America 


DERIVATIVES   FROM   BY-PRODUCT  OVENS  323 

with  the  Otto  type  next.  The  Koppers  has  vertical  and  the  Semet- 
Solvay  horizontal  flues  (Figs.  106  and  108).  The  modern  ovens  are 
of  the  regenerative  type,  that  is,  they  use  the  waste  heat,  and  live 
gas  from  the  ovens  to  heat  the  regenerators  which  in  turn  heat  the 
air  drawn  through  them  on  its  way  to  aid  combustion  in  the  flues, 
where  the  gas  from  the  ovens  is  used  to  maintain  heat.  The  direc- 
tion of  the  current  of  gas  or  air  is  reversed  about  every  half  hour 
and  in  that  way  the  regenerators  are  kept  hot. 

The  ovens  are  arranged  in  batteries  and  each  oven  is  a  steel  cham- 
ber surrounded  by  flues  and  lined  with  silica  brick.  The  batteries 
vary  in  size,  but  60  ovens  make  a  battery  in  the  large  plants  and  the 
largest  plants  have  640  or  more  ovens.  An  oven  of  a  large  type  is 
about  30  to  36  feet  long  by  10  feet  high  while  the  smaller  types  are 
only  about  6  feet  high.  The  coke  is  pushed  out  of  the  oven  by  a 
pusher  and  taken  in  cars  to  a  quenching  bath.  As  a  rule  about  8 
tons  of  crushed  coal  are  fed  into  an  oven  with  a  charging  machine 
and  it  is  fired  for  from  seventeen  to  twenty-four  hours,  depending 
upon  requirements.  A  large  plant  will  handle  between  700  and  800 
tons  of  coal  per  hour. 

Derivatives  from  by-product  ovens.  —  The  process  of  separating 
the  various  by-products  from  one  another  is  very  complicated  and  a 
vast  number  of  derivatives  are  obtainable.  (See  chart,  Fig.  5.) 
The  volatile  constituents  are  drawn  off  the  ovens  and  through  con- 
densers and  scrubbers  by  means  of  powerful  exhausters.  The  tar 
is  practically  all  eliminated  from  the  other  constituents  by  the  re- 
duction of  temperature.  The  remaining  tar  is  finally  eliminated  by 
the  impinging  method  employed  in  tar  extractors  of  the  impact  type 
in  which  the  tar  and  other  constituents  are  drawn  against  a  combina- 
tion of  perforated  and  plain  plates,  the  tar  adhering  while  the  more 
fluid  constituents  pass  on.  The  ammonia  is  removed  by  scrubbers 
in  which  water  absorbs  the  gas,  and  the  oils  are  distilled  (Fig.  108). 

The  common  products  of  the  ovens  are  coke,  gas,  tar  and  ammonia 
liquor.  The  coke  is  used  for  metallurgical,  foundry  and  heating  pur- 
poses, and  the  fines  from  the  coke,  known  as  coke  breeze  are  burned 
under  boilers  in  power  plants  or  other  steam  plants.  The  gas  may 
be  scrubbed  and  used  for  illuminating  purposes,  or  it  may  be  used  for 
heating.  In  some  cases  it  has  been  used  in  internal  combustion  en- 
gines. The  tar  is  used  to  a  large  extent  as  fuel,  in  road  making, 


I 


•4T^ 


m 


M  * 
8  «T 


(324) 


MANUFACTURE  OF  COKE   FOR  DOMESTIC  FUEL 


325 


in  waterproofing,  in  paints  and  for  other  purposes.  By  heating  it 
between  170°  C.  and  360°  C.  a  number  of  derivatives  may  be  ob- 
tained which  include  heavy  and  light  oils,  creosote,  pitch  and  other 
constituents.  The  most  important  of  the  oils  are  benzol  and  toluol, 
the  former  of  which  on  distillation  gives  a  number  of  light  oils  such  as 
gasoline  and  naphtha.  The  coal-tar  dyes  and  numerous  other  val- 
uable constituents  are  derived  by  further  distillation.  The  ammonia 
liquor  is  used  chiefly  for  the  extraction  of  sulphate  of  ammonia  by 
treatment  with  sulphuric  acid.  The  sulphate  has  extensive  appli- 
cation in  the  chemical  industries  and  in  the  manufacture  of  fertilizers. 

The  total  value  of  the  by-products  from  coke  produced  in  the 
United  States  in  1916  was  placed  at  $61,931,595  of  which  nearly  25 
million  dollars  were  obtained  from  the  benzol  and  toluol.  The  value 
of  the  coke  for  the  same  year  was  $75,373,070. 

The  following  figures  show  the  amount  of  coal  used  for  coking  in 
the  United  States,  the  average  yield  of  coke  per  cent  from  the  coal, 
and  the  value  of  the  coke,  for  the  years  1915,  1916  and  1917: 


Coal  for  ovens 

Average  percentage  yield 

Value  at  ovens 

Beehive  ovens 

1915 

42,278,516 

65-1 

$  56,945,543 

1916 

55.084,958 

64.4 

95,468,127 

1917 

52,246,612 
By-product  ovens 

63.5 

159,599,864 

1915 

19,554,382 

72.0 

48,558,325 

1916 

26,524,502 

71-9 

75,373,070 

1917 

31,505,759 

71.2 

83,752,371 

Of  the  states  of  the  Union,  Pennsylvania  far  surpasses  all  others  in 
production,  her  output  being  about  60  per  cent  of  that  for  the  country. 

Manufacture  of  coke  for  domestic  fuel.  —  Some  coke  is  now  used 
for  domestic  and  steaming  purposes,  but  80  to  90  per  cent  of  all  coke 
produced  is  used  in  the  metallurgical  industry.  There  has  been  a 
strong  desire  in  recent  years  among  men  interested  in  fuels  to  find  a 
fuel  for  domestic  purposes  with  properties  somewhere  between  those 
of  coal  and  coke. 

A  process  has  recently  been  tried  out  at  Syracuse,  New  York,  by 
Donald  Markle,  for  one  of  the  Pennsylvania  anthracite  companies, 
with  the  object  of  briquet  ting  and  coking  anthracite  fines.  Culm  is 


326  THE  PREPARATION  AND   USES  OF  COAL 

washed,  the  coal  crushed,  cemented  with  14  to  25  per  cent  of  pitch 
to  form  briquets  and  then  burned  in  an  oven.  The  product  is  known 
as  anthrocoal  and  it  is  claimed  that  the  experiments  tried  have  pro- 
duced a  very  satisfactory  domestic  fuel  which  on  test  was  20  per 
cent  more  efficient  in  a  kitchen  range  than  chestnut  coal. 

The  development  of  the  process  for  carbonization  of  coal  at  low 
temperatures  has  led  to  the  production  of  carbocoal,  a  fuel  contain- 
ing a  little  more  of  the  volatile  combustible  constituents  of  the  coal, 
than  that  contained  in  ordinary  coke,  the  ratio  being  about  3  to  i. 
It,  therefore,  approaches  anthracite  as  a  fuel  in  burning  longer,  in 
being  cleaner,  in  producing  less  smoke  and  in  standing  storage  better 
than  bituminous  or  other  coals  which  lie  below  anthracite  in  fixed 
carbon.  It  has  been  shown  by  experiment  in  Canada1  that  lignite 
may  be  satisfactorily  carbonized  and  the  coked  material,  which  is  too 
powdery  to  be  used  in  that  condition,  briquetted.  From  a  ton  of 
2000  pounds  of  this  lignite  3150  cubic  feet  of  gas,  10.2  pounds  of  am- 
monium sulphate,  5.3  imperial  gallons  of  tar,  and  910  pounds  of  car- 
bonized residue  were  obtained.  The  coal  used  contains  31.8  per 
cent  moisture.  The  carbonized  products  had  an  available  heating 
value  75  per  cent  above  that  of  the  original  coal. 

Bituminous  coal  has  been  treated  very  satisfactorily  by  carbon- 
izing it  at  low  temperature  and  briquetting  the  coke  formed.  From 
coals  running  over  32  per  cent  volatile  matter  where  carbonized  at 
850°  to  950°  P'.  the  following  constituents  have  been  obtained:2 

By-products  per  ton  of  coal 

Dry  tar   34  gallons 

Gas 8457  cubic  feet 

Ammonium  sulphate 21  pounds 

Light  oil  from  gas 1.87  gallons 

Other  tar  oils .  . 19.3  gallons 

Pitch,  per  cent  of  tar 43 

The  average  analysis  of  the  briquets  made  from  the  residue  is  as 

follows: 

Volatile  matter 3.8  per  cent 

Fixed  carbon 85 .  i       " 

Ash n. i       " 

1  Stansfield,  Edgar,  Carbonization  of  Canadian  lignite.    Jour.  Ind.  and  Eng.  Chem., 
Vol.  13,  p.  17,  1921. 

2  Curtis,  H.  A.,  The  commercial  realization  of  the  low-temperature  carbonization  of 
coal.    Jour.  Ind.  and  Eng.  Chem.,  Vol.  13,  p.  23,  1921. 


MANUFACTURE  OF   COKE  FOR  DOMESTIC  FUEL  327 

The  production  of  such  fuels  has  been  put  on  a  commercial  basis 
within  the  last  couple  of  years.  A  description  of  a  plant  at  Clinch- 
field,  Virginia,  capable  of  treating  500  tons  a  day  has  been  published 
by  Eshereck.1  In  this  plant  there  are  24  primary,  low-temperature, 
and  10  high- temperature  retorts.  The  primary  retorts  are  arranged 
in  four  batteries  and  the  crushed  coal  is  fed  into  them  from  overhead 
bins.  The  semi-carbocoal  is  taken  from  these  retorts,  which  are  con- 
tinually in  operation  and  carried  to  storage  bins  in  the  briquetting 
plant.  It  is  then  ground,  mixed  with  pitch,  fluxed  and  briquetted 
on  heavy  roll  presses.  The  briquets  are  carried  on  a  long  conveyor 
and  then  by  a  steel  charging  car  to  the  secondary  retorts.  The 
finished  briquets  are  dumped  from  the  secondary  retorts,  which  are 
inclined,  and  later  quenched. 

The  by-products  are  carried  through  the  same  general  process  of 
condensing,  scrubbing  and  distilling  as  in  the  other  by-product 
processes  described  above.  The  process  outlined  is  known  as  the 
Smith  Process.  It  is  found  that  the  yield  of  carbocoal  runs  from  65  to 
72  per  cent  of  the  coal  used,  depending  upon  the  character  of  the  coal, 
and  on  account  of  the  low  temperatures  at  which  the  primary  retorts 
are  heated  there  is  a  much  greater  yield  of  tar  oils  than  in  ordinary 
by-product  operations.  In  some  cases  it  is  over  seven  times  as  great. 
There  is  practically  no  production  of  pitch,  but  the  other  constituents 
are  similar  in  quantity  to  those  derived  from  a  by-product  coke  oven. 

It  seems  very  probable  that  this  method  of  producing  fuel  will 
have  a  rapid  development  and  that  in  the  future  practically  all  of 
our  fuels  will  be  treated  in  some  such  manner.  It  is  also  probable 
that  some  of  the  liquid  by-products  obtained  from  this  process  will 
be  used  in  our  homes  as  domestic  fuel. 

1  Eshereck,  George,  Jr.,  Prospect  that  soon  no  coal  will  be  used  without  preliminary 
devolatilization.  Coal  Age,  Vol.  18,  p.  327,  1920. 


CHAPTER  XII 

THE   GEOLOGIC   AND   GEOGRAPHIC   DISTRIBUTION 

OF  COAL 

From  a  geological  standpoint  coal  is  distributed  through  the  vari- 
ous formations  from  the  Upper  Devonian  to  the  Pleistocene  although 
the  latter  contains  only  low-grade  coal  and  the  former  a  very  limited 
quantity.  In  the  later  Pleistocene  and  the  Recent  rocks  large  beds 
of  peat  not  yet  changed  to  coal  are  found  in  many  countries. 

The  earliest  coal  deposits  known  are  in  the  Upper  Devonian  in 
northern  Russia  and  on  Buren  Island,  Norway,  and  they  are  coincid- 
ent with  the  first  great  development  of  land  plants  on  the  earth. 
Between  the  Devonian  and  Pleistocene  there  is  not  a  geological  system 
without  at  least  some  coal  somewhere  on  the  globe.  Certain  systems, 
however,  carry  the  bulk  of  the  valuable  coal.  Taking  the  earth  as 
a  whole  the  Carboniferous  is  the  most  important  for  high-grade  coal 
while  the  Tertiary  contains  most  of  the  lignite.  The  Mississippian, 
or  Lower  Carboniferous,  as  it  is  known  outside  of  the  United  States, 
carries  valuable  coal  in  Virginia,  Scotland,  Spitzbergen,  Russia, 
Corea  and  Manchuria.  The  Permian  is  very  important  in  the  South- 
ern Hemisphere,  particularly  in  Australia,  India  and  Africa,  and  this 
system  also  carries  some  coal  in  Europe,  the  United  States  and  eastern 
Asia.  The  Triassic  is  a  prominent  coal-bearing  system  outside  of 
America  as  it  contains  the  coal  of  Tasmania,  some  in  Queensland  and 
New  South  Wales,  Australia,  considerable  in  Hungary,  Austria, 
Japan,  China  and  South  Africa  and  a  small  field  in  North  Carolina  and 
Virginia,  in  the  eastern  United  States.  The  Jurassic  is  not  important 
in  America  outside  of  Alaska  and  small  areas  in  the  Yukon  but  it 
is  of  great  importance  in  China  and  Corea,  and  it  is  also  coal-bearing 
in  New  Zealand  and  Austria.  The  Upper  Cretaceous  is  one  of  the 
great  coal-bearing  periods  in  the  earth's  history  especially  in  western 
North  America  and  Central  Europe,  while  the  Lower  Cretaceous,  or 
Comanchean  of  some  of  the  United  States  geologists,  except  in  its 

328 


GEOLOGIC  AND   GEOGRAPHIC  DISTRIBUTION  329 

earlier  formations,  is  probably  the  most  barren  of  coal  of  all  the 
systems  from  the  Lower  Carboniferous  onward.  It  carries  good 
coal  in  western  Canada  and  in  limited  areas  in  the  western  states,  a 
little  in  South  Australia,  and  low  grade  bituminous  coal  in  Spain. 
The  abundance  of  coal  in  the  Upper  Cretaceous  and  Tertiary,  follow- 
ing its  scarcity  in  the  Lower  Cretaceous  repeats  the  conditions  exist- 
ing in  the  Lower  and  Upper  Carboniferous.  The  Lower  Carbon- 
iferous and  the  Lower  Cretaceous  were  periods  of  extension  of  the  sea 
over  the  continents,  except  in  the  earlier  stages  of  the  Lower  Creta- 
ceous when  many  lakes  and  swamps  existed,  while  it  gradually  with- 
drew during  the  following  periods  leaving  great  flat  areas  covered 
with  swamps,  as  in  the  case  of  our  coastal  plains  of  the  present  day. 
Extension  of  the  sea  and  marine  deposition  or,  on  the  other  hand,  very 
high  lands  with  rapid  erosion  do  not  go  together  with  coal  formation, 
but  the  gradual  restriction  of  the  sea  and  the  formation  of  coal  work 
together  harmoniously. 

The  period  of  coal  formation  begun  in  the  Upper  Cretaceous  con- 
tinued into  the  Tertiary  and  most  of  the  lignite  of  the  world  was 
formed  in  that  period.  Every  continent  contains  some  coal  of  this 
age  and  America  and  Europe  have  very  large  supplies.  There  is 
some  good  anthracite  and  bituminous  coal  of  Tertiary  age  but  most 
of  the  coal  outside  of  the  mountain  regions  is  of  the  lignite  type  be- 
cause it  has  not  been  changed  to  a  higher  form  by  heat  or  pressure 
or  by  these  two  agencies  combined. 

As  to  the  occurrence  of  coal  in  rocks  older  than  the  Upper  Devon- 
ian, the  question  is  often  asked  why  coal  should  not  exist  in  these 
older  formations.  The  only  explanation  is  that  the  land  plants  had 
not  reached  a  stage  in  their  evolution  which  made  them  sufficiently 
abundant  and  widely  distributed  to  form  extensive  deposits  of  coal. 
Deposits  of  vegetal  matter  were  made  in  earlier  formations,  even 
back  in  the  pre-Cambrian,  as  shown  by  beds  of  black  shales  and 
deposits  of  graphite,  but  these  were  of  quite  limited  extent  and  ap- 
parently made  from  aquatic  plants.  It  is  also  true  that  from  the  close 
of  the  pre-Cambrian  until  the  Carboniferous  not  only  the  American 
continent  but  some  of  the  others  as  well  were  largely  covered  with  the 
sea  and  marine  deposits  were  the  main  types  being  formed.  It  re- 
quires proper  topographic  conditions  as  well  as  an  abundance  of  land 
plants  to  produce  coal. 


330 


GEOLOGIC   AND    GEOGRAPHIC   DISTRIBUTION 


TABLE  OF   GEOLOGICAL  FORMATIONS  USED   IN   AMERICA, 

EUROPE  AND   AUSTRALIA   WITH   SPECIAL  REFERENCE 

TO    COAL-BEARING    SERIES 


- 

America 

Great  Britain 

France 

Germany 

Australia 

0 

1 

R.ecent 

Recent 

Recent 

Alluvium 

decent 

's 

o 

Pleistocene 

Pleistocene 

Pleistocene 

Pleistocene  or 

3leistocene 

§ 

Diluvium 

0 

Pliocene 

Pliocene 

Pliocene 

Pliocan 

3liocene 

13 

Miocene 

Miocene 

Miocene 

Miocan 

Miocene 

1 

Oligocene 

Oligocene 

Oligocene 

Oligocan 

Oligocene 

H 

Eocene 

Eocene 

Eocene 

Paleocan 

Socene 

Cretaceous  (Upper) 

Cretaceous  (Upper) 

Cretacique 

Kreide 

Cretaceous 

(Upper) 

(i)  Laramie 

(i)  Upper  Chalk 

Neocretacique 

Ober  Kreide 

(2)  Montana 

(2)  Lower  Chalk 

(3)  Colorado 

(3)  Marls 

(4)  Dakota 

(4)  Upper      Green- 

sand 

(5)  Gault 

Comanchean  or 

Cretaceous  (  Lower  }  f  Eocretacique 

Unter-Kreide 

Cretaceous 

Lower  Cretaceous 

(i)  Lower     Green- 

(i)  Gault 

(Lower) 

0 

sand 

1 

(2)  Wealden 

(2)  Weald 

1 

Jurassic 

Jurassic 

Jurassique 

Jura 

furassic 

(i)  Upper 

(i)  Oolite 

(i)  Neojurassique 

(i)  Malm 

(2)  Middle 

(2)  Lias 

(2)  Mesojurassique 

(2)  Dogger 

(3)  Lower 

(3)  Eojurassique 

(2)  Lias 

Triassic 

(Newark  series) 

Triassic 

Friassique 

Trias 

Triassic 

(i)  Rhaetic 

(i)  Rhaetic 

(2)  Keuper 

(2)  Keuper 

(3)  Bunter 

(3)  Muschel- 

t 

kalk 

(4)  Bunter 

GEOLOGIC   AND    GEOGRAPHIC   DISTRIBUTION 

TABLE   OF   GEOLOGICAL   FORMATIONS    (Continued) 


331 


America 

Great  Britain 

France 

Germany 

Australia 

Permian  (Dunkard) 

Permian  or  Dyas 

Permien 

Perm 

Permo-Carbon- 

iferous 

(a)  Thuringien 

(a)  Zechstein 

(a)  Igneous   series 

Upper  Barren 

(b)  Saxonien 

(b)  Rothlie- 

(b)  Upper  or 

Measures 

gende 

Newcastle 

(c)  Atunien 

Coal  Measures 

/    \       y% 

Carboniferous 

Carboniferous 

Carboniferien 

Karbon 

^6^    .L/empsey 
series 

(d)  Middle  Coal 

(l)  Pennsylvanian 

(i)  Upper  Carbon- 

Oberkarbon 

Measures 

or  Upper  Car- 

iferous 

(«)  Upper  Ma- 

boniferous 

rine  Series 

(a)  Monongahela 

(/)  Lower  or 

or  Upper  Pro- 

(a) Stephanien  or 

(a)  Ottweiler 

Greta  Coal 

ductive 

Ouralien 

Measures 

Measures 

(b)  Westphalien  or 

(b)  Saarbrucken 

(g)  Lower  Ma- 

(b) Conemaugh 

Muscovien 

rine  Series 

.0 

or  Lower  Bar- 

(a) Coal  Measures 

8 

ren  Measures 

1 

(c)  Allegheny  or 

2 

-  Lower  Produc- 

tive Measures 

(d)  Pottsville  or 

(b)  Millstone  Grit 

(c)  Namurien 

Millstone  Grit 

(2)  Mississippian 

(2)  Lower  Carbon- 

Dinantien 

Unterkarbon 

Carboniferous 

or  Sub-Car- 

iferous; Culm, 

Kulm  or  Koh- 

boniferous 

or  Limestone 

lenkalk 

(a)  Mauch  Chunk 

series 

(b)  Pocono 

Devonian 

Devonian 

Devonienne 

Devon 

Devonian 

Silurian 

Silurian 

Silurien 

Ober-Silur 

Silurian 

Ordovician 

Lower  Silurian 

(i)  Goth-Landien 

Unter-Silur 

Ordovician 

(2)  Ordovicien 

Cambrian 

Cambrian 

Cambrien 

Kambrium 

Cambrian 

1 

Proterozoic  or 

Pre-Cambrien  or 

Eozoisch  or 

Algonkian 

.0 

Algonkian 

Archeen 

Archaozoisch 

| 

Archaeozoic  or 

Archean 

Archean 

1 

Archean 

332 


GEOLOGIC  AND   GEOGRAPHIC  DISTRIBUTION 


The  following  table  shows  the  geological  distribution  of  the  different 
types  of  coal  on  the  various  continents  and  their  relative  abundance. 
More  detailed  tables  are  given  for  the  individual  continents  where  the 
coal  resources  of  those  continents  are  described. 

TABLE  SHOWING  THE  GEOLOGICAL   DISTRIBUTION   OF 
COAL  BY  VARIETIES 


Period 

North 
America 

South 
America 

Europe 

Asia 

Africa 

Oceania 

Quaternary  

1 

1 

1 

1 

1 

Tertiary  

SBLAB 

BLB 

BL 

BBL 

L 

L 

Cretaceous  

ABLBS 

BB 

BL 

b 

B 

1 

Jurassic  and  Triassic 

ablb 

a 

B  1 

ASBL 

B 

aB 

Permian 

b 

b 

A  B 

B 

B  c 

B 

Permo-Carboniferous 

b 

ABB 

AB1 

BB 

Carboniferous  

ABSB 

ABcl 

AS 

b 

Lower  Carboniferous  . 

aBs 

ABS 

B 

Devonian  

b 

A,  Anthracite;  S,  Semibituminous;  B,  Bituminous;  B,  Subbituminous;  L, 
Lignite,  including  brown  coal;  C,  Cannel.  Capital  letters  are  used  to  indicate 
large  and  important  deposits  and  lower  case  for  small  or  unimportant  deposits 
of  the  same  variety 

Geographically,  coal  is  almost  universally  distributed  as  there  are 
very  few  countries  which  do  not  have  some  coal.  •  Even  Antarctica 
has  a  considerable  supply.  There  are  a  few  countries,  including 
Egypt,  Thibet  and  Bolivia,  which  do  not  report  any  workable  de- 
posits. Norway  has  little  or  none  outside  of  Spitzbergen  and  her 
other  northern  islands.  Switzerland  has  had  very  small  supplies 
and  they  are  said  to  be  nearly  exhausted.  Many  other  countries 
have  very  little  coal  in  proportion  to  their  political  importance. 
Such  are,  for  example,  Italy,  Roumania,  Sweden,  Brazil  and  the  Argen- 
tine Republic.  Japan  is  poorly  supplied  in  proportion  to  her  popula- 
tion and  she  will  no  doubt  expect  to  control  large  areas  on  the  main- 
land of  Asia  to  take  care  of  her  industrial  development,  because  history 


GEOLOGIC  AND    GEOGRAPHIC   DISTRIBUTION 


333 


has  shown  that  the  accessibility  of  large  coal  supplies  is  an  essential 
factor  in  the  great  industrial  development  of  any  country.  A  glance 
at  the  table  showing  the  coal  resources  of  the  various  continents  will 
show  that  Africa  and  South  America  are  not  well  supplied  with  coal, 
although  no  doubt  further  geological  work  on  these  continents  will 
reveal  much  larger  resources  than  are  here  indicated.  North  Amer- 
ica is  lavishly  supplied,  and  Europe,  Australia  and  eastern  Asia  have 
plenty.  The  distribution  of  the  coal  deposits  will  have  a  very  im- 
portant bearing  on  the  future  economic  history  and  commercial 
relations  of  these  continents  and  especially  on  those  of  certain 
countries.  This  is  well  illustrated  by  the  international  problems 
arising  from  the  distribution  of  coal  during  the  war  and  immediately 
following  it. 

The  following  table  will  show  the  coal  resources  of  the  world  by 
continents,  in  so  far  as  geological  data  exist  regarding  them.  This 
is  the  best  and  most  complete  estimate  which  has  so  far  been  com- 
piled. 

0)  COAL  RESOURCES  OF  THE  WORLD  BY  CONTINENTS 
(In  million  metric  tons;  i  metric  ton  =  i  .1023  short  tons) 


Class  A 

Classes  B  and  C 

Class  D 

Anthracite  and 
some  dry  coals 

Bituminous  coals 

Subbituminous, 
brown  coals  and 
lignites 

Totals 

Oceania  .  . 

6cq 

1  33  4.8l 

36  27O 

I7O  4.IO 

Asia  
Africa  

407,637 

11,662 

760,098 
4.c>.123 

111,851 
I  O<4. 

1,279,586 
e>7  83Q 

America  

22,542 

2,271,080 

2  811  906 

5TQC    C28 

Europe  

<?4,346 

603,162 

36  682 

784.  IQO 

Totals 

4.Q6  84.6 

3QO2  Q4.4. 

^»yy/>/uo 

toy/too^ 

(l)  From  the  Coal  Resources  of  the  World.  Twelfth  International  Geologi- 
cal Congress,  Morang  &  Company.  For  detailed  discussion  of  classes  of  coal 
see  Classification  of  Coals,  Chapter  V..  The  above  estimates  include  all  seams  i 
foot  and  over  in  thickness  and  less  than  4000  feet  deep;  and  2  feet  and  over  in 
thickness  and  between  4000  and  6000  feet  below  the  surface. 

The  outstanding  features  indicated  in  this  table  are  the  tremendous 
amount  of  coal  in  America  and  anthracite  in  Asia.  The  latter  is 
mostly  in  China.  It  seems  probable,  however,  that  much  coal  has 


334  GEOLOGIC   AND    GEOGRAPHIC   DISTRIBUTION 

been  classed  as  anthracite  in  China  which  will  turn  out  to  be  semi- 
bituminous  or  high-grade  bituminous  coal.  Nevertheless,  China  far 
surpasses  all  other  countries  combined  in  her  resources  in  this  variety 
of  coal.  America  has  little  anthracite  in  comparison  with  her  re- 
sources in  bituminous  and  brown  coals. 

The  following  table  from  Mineral  Industry  shows  the  coal  produc- 
tion of  the  various  countries  of  the  world  from  the  year  1911  to  1916. 
During  the  war  the  production  of  some  countries  almost  ceased  and 
since  the  beginning  of  the  war  it  has  been  impossible  to  secure  accurate 
data  concerning  the  production  of  many  countries.  As  indicated  by 
the  table,  the  output  of  the  United  States  has  increased  rapidly  and 
her  production  has  almost  passed  the  6oo,ooo,ooo-ton  mark.  She 
has  also  become  the  leading  exporter  of  coal  since  the  exports  of 
Great  Britain  have  decreased  from  over  75,000,000  tons  before  the 
war  to  less  than  20,000,000  in  1919,  while  those  of  the  United  States 
have  more  than  doubled  and  are  now  said  to  be  over  30,000,000  tons 
per  annum.  Few  of  the  great  industrial  countries  can  look  forward 
to  exporting  high-grade  coal  in  very  large  quantities  for  an  indefinite 
period  because  of  the  rate  of  increase  in  domestic  requirements  and 
the  exhaustion  of  the  more  accessible  seams. 


GEOLOGIC  AND   GEOGRAPHIC  DISTRIBUTION 


335 


0)  COAL  PRODUCTION   OF  THE  WORLD   IN   SHORT  TONS 
FOR  YEARS   1911-1916 


Country  or  State       1911 

1912 

1913 

1914 

1915 

1916 

United  States  496,371,126 
Great  Britain  304,518,927 
Germany  258,223,763 
Austria-Hungary  .  .  54,960,298 
France  43,242,778 

534.466,580 
291,666,299 
281,979,467 
56.954,279 
45,534.448 
33.775.754 
25.322,851 
21,648,902 
16,471,000 
16,534,500 
14,512.829 
10,897,134 
7,591,619 
4,559,453 
2.438,929 
1,901,902 
1,470,917 
1,010,426 
982,396 

940,174 
909.293 
73L720 
664,334 
525,459 

622,669 
471,259 
397,149 
335.OOO 
330,488 
307,461 
306,941 
324,511 
216,140 

59,  987 

16,938 
(a)    .12,000 

2,998 

569,960,219 
321,922,130 
305,714,664 
59,647,957 
45,108,544 
37.188,480 
25,600,960 
23,988,292 
18,163,856 
15,432,200 
15,012,178 
11,113,865 
8,191,243 
4,731,647 
2,115,834 
2,064,608 
1,362,334 
1,162,497 

927,244 

772,802 
668,524 
609,973 

453,136 
401,199 

351,687 
301,970 

237,728 

61,648 
49,762 

27,653 
13,355 

513,525,477 
297,698,617 
270,594,152 
(d)  53,396,400 
33.360,885 
36,414,560 
(a)  19,000,000 
21,700,572 
18,430,974 

13,594,984 
11,663,865 
7,778,706 
4,897,360 
2,548,664 
1,928,540 

1,180,825 

861,265 
691,640 
699,217 

440,905 
404,143 

357,515 
312,897 

391,394 

68,130 
128,505 

32,743 

531.619.487 
283.570,560 
259,139.786 
(d)  52,679,712 
19,908,892 
31,158,400 
15,691,465 
22,596,750 
19,156,404 

13,269,023 
10,582,889 
9,275,083 
5,414,475 
2,208,624 
2,262,148 

1,147,186 

1,042,748 
588,104 
727,531 

454,432 

321,066 
318,563 

458,934 
66,000 

597,474,000 
287,110,153 

50,801,602 

(c)  22,000,000 
28,962,724 

(a)  19,900,000 
22,189,969 
19.325,637 
(o)  24,000,000 
14,461,678 
11,262,420 
11,200:370 

6.05/.727 
2,527,991 

I  016,654 

1,439,538 
463,074 

457,262 

337,709 
35L703 

491,532 
62,244 

Russia  29,361,764 
Belgium                     25  411,917 

Japan                       19.436,536 

India                         13.494.  573 

China      16,534,500 

Canada             .    .    .11,323,388 

New  South  Wales  .  .9,374,596 
Transvaal  (&)  7,112,254 

Spain  4,316,245 

New  Zealand  2,315,390 
Holland  1,628,097 

Chile                          i  277  191 

Queensland  998,556 
Mexico                  (a)  1,400,000 

Bosnia  and  Herze- 
govina    848,510 

Turkey  799,168 

Italy  614,132 
Victoria  732,328 
Orange  Free  State  (e)  482,690 
Dutch  East 
Indies  (a)  600,000 
Indo-China             (a)  460  ooo 

Sweden                          343  707 

Servia  .                        335  495 

Western  Australia  (a)  300,000 
Peru  (o)  300  ooo 

Formosa  280,999 
Bulgaria  270,410 

Rhodesia  212,529 

Korea  138,508 

Tasmania                  (a)  70  ooo 

British  Borneo  (a)  100,000 
Spitzbergen  .  .               44  092 

Brazil  16  535 

Portugal  (a)  10,000 

Venezuela  (a)  10,000 
Switzerland  8,267 
Philippine  Islands.  .  (a)  2,000 
Unspecified  (0)1,016,947 

Totals.        .  1,309,574,000 

(c) 
1,377,000,000 

(c) 
1,478,000,000 

(c) 
1,334,000,000 

(c) 
1,270,000,000 

(J)   From  Mineral  Industry,  1917. 

(o)  Estimated,  (b)  Transvaal,  includes  Natal  and  Cape  of  Good  Hope  and  figures  are  only  for 
coal  sold,  (c)  Approximate.  (d)  Hungarian  production  estimated  at  10,000,000  short  tons,  (e) 
Represents  only  coal  sold,  probably  10  to  12  per  cent  less  than  production. 


CHAPTER  XIII 
THE   COAL  FIELDS   OF   THE   WORLD  —  AMERICA 

Introduction 

America  is  here  considered  as  two  units  —  North  and  South. 
America  undoubtedly  has  the  greatest  coal  deposits  of  the  world, 
but  it  is  a  striking  fact  that  so  far  as  our  knowledge  of  the  resources 
of  the  two  continents  extends  the  southern  contains  only  about 
six-tenths  of  one  per  cent  as  much  coal  as  the  northern  continent. 
A  better  knowledge  of  the  geology  of  South  America  will  no  doubt 
extend  her  known  resources  but  the  disparity  between  the  future 
supplies  of  the  two  continents  will  profoundly  affect  their  trade 
relations. 

North  America 

In  a  discussion  of  North  America's  coal  deposits  there  are  included 
those  of  Canada,  Newfoundland,  the  West  Indies,  the  United  States, 
including  Alaska,  Cuba,  Mexico  and  Central  America.  The  following 
table  shows  the  relative  resources  of  these  countries  in  so  far  as  we 
have  reasonably  definite  knowledge  regarding  them.  Mexico  has 
considerable  good  coal  but  her  resources  are  not  well  known  outside 
of  a  few  areas  explored  by  American  or  European  companies. 

This  table  shows  the  great  extent  of  the  coal  supplies  of  the  United 
States  in  those  types  of  coal  which  are  used  so  much  in  the  industries. 
Canada  is  also  unusually  well  supplied  with  bituminous  coal  and  with 
lower  grades  but  she  is  deficient  in  anthracite  and  in  related  high- 
carbon  coals.  This  deficiency  will  probably  not  be  so  keenly  felt  in  the 
future,  however,  as  it  has  been  in  the  past,  because  with  the  develop- 
ment of  the  use  of  partially  devolatilized  fuels  such  as  carbocoal  a 
substitute  for  anthracite  will  be  provided  in  many  parts  of  the  country. 
The  coal  deposits  of  Canada  and  the  United  States,  especially  of  the 
latter,  have  been  gone  over  fairly  well,  and  the  above  estimate  of  the 
resources  may  be  regarded  as  comparatively  accurate.  Considerable 

336 


NORTH  AMERICA 


337 


changes  will  be  made,  however,  in  these  figures  as  more  geological 
work  is  done,  particularly  in  those  for  Canada  since  there  are  very 
large  areas  in  Canada  on  which  little  field  work  has  been  completed. 

ESTIMATE   OF   THE   COAL  RESOURCES  OF   NORTH   AMERICA 
(In  million  metric  tons;  i  metric  ton  =  i  .1023  short  tons) 


Class  A 

Classes  B  and  C 

Class  D 

Anthracite    and 
some  dry  coals 

Bituminous 
coals 

Subbituminous 
coals,  brown  coals 
and  lignites 

Totals 

Ne  wf  oundland  . 

500 

500 

Canada  
United  States  .  .  . 
Central  America 

2,158 
19.684 

283,661 

i,955,52i 

i 

948,450 
1,863,452 
4 

1,234,269 
3,838,657 
5 

Total  

21,842 

2,239,683 

2,811,906 

Z,  O73,  4^1 

Table  from  The  Coal  Resources  of  The  World,  Morang  &  Co.,  1913.  A  detailed 
statement  regarding  the  different  classes  of  coal  may  be  found  in  Chapter  V 
on  Classification  of  Coals.  The  estimates  include  all  seams  i  foot  and  over 
in  thickness  and  4000  feet  or  less  in  depth;  and  all  seams  2  feet  and  over  in  thick- 
ness and  between  4000  and  6000  feet  in  depth. 

The  geological  age  of  the  coals  in  North  America  ranges  from 
Mississippian,  or  Sub-Carboniferous,  to  Pleistocene,  the  main  periods 
for  their  formation  being  the  Upper  Carboniferous,  or  Pennsylvanian, 
the  Cretaceous,  and  the  Tertiary.  The  table  given  below  shows  their 
geological  distribution. 


338  THE   COAL  FIELDS  OF  THE  WORLD— AMERICA 

GEOLOGICAL  AGE  OF  COALS  OF  NORTH  AMERICA 


Canada 

United  States 

Newfoundland 

Mexico 

Central  America 

Trinidad 

ri 

o3 
> 
O 
£ 

New  Brunswick 

Ontario 

Manitoba 

Saskatchewan 

3, 

1 

1 
1 

Yukon  Territory 

N.  W.  Territory 

o 

J- 

11 

F 

Atlantic  Coast 
Region 

Interior  Province 

P 

Great  Plains 
Province 

Rocky  Mountain 
Province 

Pacific  Coast 
Province 

i 

Pleistocene 

1 

. 

— 



1 
1 

Pliocene  

Miocene  

1 

1 

aAB 

Eocene  

b 

1 

1 

L 

B 
L 

L 

L 

BL 

BL 

BL 

aa 
BB 
L 

bBL 

Tertiary  undifferen- 
tiated 

1 

b 
1 

b 

L 

1 



b 

BB 

L 

AA 
BB 



Upper  Cretaceous  

B 

b 

L 

b 

B 

1 

B 

BB 

Lower  Cretaceous  

a 
A 
B 

S 

B 

S 

B 

B 

B 

Jurassic  

bBl 

Triassic  

a 
a 

9 

aB 

Permian 

b 

b 

Pennsyl  vanian  

B 

B 

b 

aA 

BS 

B 

b 

Mississippian  

b 

B 

C 

aa 

S 

B 

A.  Anthracite;  A.  Semianthracite;  S.  Semibituminous;  B.  Bituminous;  B.  Subbituminous;  L. 
Lignite  and  brown  coal.  Capital  letters  indicate  important  deposits  and  lower  case  relatively  unim- 
portant to  unworkable  deposits  of  the  same  type. 


COAL  AREAS  OF  CANADA 


PLATE  XI.  —  The  Coal-fields  of  Canada.   (i 


D.  B.  Bowling  Canadian  Geological  Survey.) 


THE   COAL  DEPOSITS  OF   CANADA 


339 


THE  COAL  DEPOSITS  or  CAN  AD  A1 

The  production,  and  the  geological  age,  of  the  coals  of  Canada 
have  been  given  in  the  preceding  tables  and  the  following  table  sums 
up  the  distribution  and  the  characters  of  the  coals  in  the  various 
provinces  as  worked  out  by  D.  B.  Dowling. 

COAL  RESOURCES  OF  CANADA 


District 

Actual  Reserve 
Calculation  based  on  actual  thick- 
ness and  extent 

Probable  Reserve 
(Approximate  estimate) 

Area    Sq. 
Miles 

Class  of 
coal 

Metric  tons 
(i  metric  ton  = 
1.1023  short  tons) 

Area  Sq. 
Miles 

Class  of 
coal 

Metric  tons 

B2 

2,137,736,000 

B2 

4,891,817,000 

Nova  Scotia    .  .  . 

174.31 

273  .  5 

C 

50,415,000 

C 

20,000,000 

New  Brunswick.  . 

121 

B2 

151,000,000 

Ontario  

10 

D2 

25,000,000 

Manitoba  

48 

D2 

160,000,000 

Saskatchewan  

306 

D2 

2,412,000,000 

13,100 

D2 

57,400,000,000 

D2 

D2 

^26,450,000,000 

DX 

382,500,000,000 

DI 

464,821,000,000 

Alberta. 

25,300 

Bs 

1,197,000,000 

56,375 

Bs 

139,161,000,000 

B2B! 

2,026,800,000 

B2Bi 

43,022,600,000 

\ 

A2 

669,000,000 

A2 

100,000,000 

A2B2 

23,653,242,000 

A2B2 

40,807,700,000 

British  Columbia 

439     j 

Bs 

118,000,000 

5,595 

Bs 

2,300,000,000 

D2 

60,000,000 

DiD2 

5,136,000,000 

C 

1,800,000,000 

Yukon  

2,840 

A2Bs 

250,000,000 

North-West 

Territories  

300 

DiDz 

4,690,000,000 

D2 

4,800,000,000 

Arctic  Islands  

6,000 

B2Bs 

6,000,000,000 

C 

Totals  

26,219.31 

*4l4,8o4,l93,ooo 

82,662.5 

801,966,117,000 

*  20,000,000  tons  deducted  for  the  amount  of  coal  already  exhausted  in  Alberta.  Table  from  Coal 
Resources  of  the  World.  For  details  of  classes  of  coal  see  Classification  of  Coals,  Chapter  V.  This  table 
contains  all  seams  of  I  foot  or  over  to  a  depth  of  4000  feet. 

1  For  detailed  accounts  of  the  coal  deposits  of  Canada  see  The  Coal  Resources  of  the 
World,  Twelfth  International  Geological  Congress,  (Morang  &  Co.),  An  Economic  In- 
vestigation of  the  Coals  of  Canada,  by  J.  B.  Porter  and  R.  J.  Durley,  Department  of 
Mines,  Canada;  The  Coals  of  Canada, by  D.  B.  Dowling,  Memoir  59,  Canadian  Geol. 
Survey,  1915;  and  The  Coal  Fields  of  British  Columbia,  by  D.  B.  Dowling,  Memoir  69, 
Canadian  Geol.  Survey,  1915. 


340  THE   COAL  FIELDS  OF  THE  WORLD— AMERICA 

In  addition  to  the  figures  mentioned  here  there  might  be  added 
17,499,000,000  metric  tons  of  coal  of  Class  B2  which  occurs  in  seams 
over  2  feet  thick  lying  at  a  depth  between  4000  and  6000  feet,  in  the 
provinces  of  Nova  Scotia,  Alberta  and  British  Columbia. 

From  the  accompanying  map  (Plate  XI)  it  will  be  observed  that 
the  coal  deposits  of  the  Dominion  are  almost  all  located  in  the  ex- 
treme eastern  and  in  the  western  parts  of  the  country.  Quebec  and 
Ontario,  the  most  populous  and  the  most  important  of  the  prov- 
inces commercially  have  no  good  coal  and  they  receive  most  of  their 
supply  from  the  United  States.  Quebec  is  without  coal  of  any  kind 
and  Ontario  has  a  few  million  tons  of  low-grade  lignite  in  the  inter- 
glacial  deposits  south  of  James  Bay.  Nova  Scotia  on  the  east  and 
Alberta  and  British  Columbia  on  the  west  have  high-grade  coal  in 
large  quantities  while  Saskatchewan  and  Alberta  have  very  large 
resources  in  lignite  and  subbituminous  coal. 

Nova  Scotia.  —  The  coal  of  Nova  Scotia  is  all  of  Pennsylvanian, 
or  Upper  Carboniferous,  age  except  for  thin  and  unmined  seams  in 
the  Mississippian,  or  Lower  Carboniferous.  Thin  seams  occur  in 
the  Millstone  grit  but  most  of  the  coal  lies  above  this  formation. 
There  are  five  important  areas  producing  coal  —  the  Joggins  and 
Springhill  areas  in  the  Cumberland  field;  the  Pictou,  Inverness 
and  Cape  Breton,  or  Sydney,  fields.  In  the  Joggins  area  there  are 
two  seams  3  to  5  feet  in  thickness,  and  the  beds  are  inclined  at  angles 
of  as  much  as  50°.  The  coal  is  of  fairly  good  quality  but  is  high  in 
ash.  This  area  has  been  famous  for  its  buried  Carboniferous  trees 
which  are  abundant  in  the  sandstones  of  the  Coal  Measures.  The 
Springhill  area  is  considerably  faulted  and  it  seems  to  represent  the 
central  part  of  the  basin  in  which  the  Joggins  seams  were  laid  down. 
There  are  a  number  of  seams  of  which  five  can  be  mined  and  they 
make  up  a  total  of  about  50  feet  of  coal,  the  thickest  seam  reaching 
13  feet.  In  the  Pictou  field  there  is  a  little  coal  in  the  Millstone  grit 
and  in  the  Permian,  but  all  the  workable  coal  occurs  in  the  Coal 
Measures  proper,  in  two  large  fault  blocks.  One  fault  has  a  down- 
throw of  about  2600  feet.  There  are  four  seams  in  the  Westville 
area  of  this  field  varying  from  6  to  18  feet  in  thickness  and  separated 
from  one  another  by  from  90  to  260  feet  of  strata  including  some 
beds  of  oil  shales.  As  a  rule  the  beds  dip  gently.  In  the  Stellar  ton 
area  of  the  Pictou  field  there  are  9  seams,  some  of  which  are  very 


NOVA   SCOTIA  341 

thick.  The  Main  seam  varies  from  about  6  feet  to  45  feet  in  thick- 
ness and  the  Deep  seam  from  20  to  33  feet.  The  other  seams  are 
rather  thin.  There  is  one  bed  of  oil  shale  with  a  coal  seam,  in  this  area. 
It  is  5  feet  in  thickness  and  it  was  formerly  mined  for  the  extraction 
of  oil. 


FIG.  109.  —  Allen  Shaft,  near  Stellarton,Pictou  coal  field,  Nova  Scotia. 
(Photo  by  H.  Ries.) 

The  Inverness  field  is  largely  under  the  sea.  The  measures  dip 
seaward  at  from  12°  to  over  75°-and  the  seams  mined  run  about  6  to 
7  feet  in  thickness. 

In  the  Sydney  field,  which  occupies  the  northern  part  of  Cape 
Breton  County  the  Coal  Measures  dip  gently  seaward,  being  disturbed 
by  only  small  folds.  They  have  been  mined  on  the  slope  under  the 
sea  for  more  than  a  mile  from  the  shore.  The  number  of  seams  in 
this  field  varies  from  i  to  12  with  an  aggregate  thickness  of  coal 


342 


THE   COAL  FIELDS  OF  THE   WORLD— AMERICA 


from  i  foot  to  46  feet.     It  is  expected  that  the  workings  will  in  time 
extend  nearly  3  miles  from  the  shore. 

New  Brunswick.  —  In  New  Brunswick  the  upper  members  of  the 
Pennsylvanian  are  lacking.  The  Millstone  grit  is  widely  distributed 
over  the  province  and  it  contains  a  few  thin  seams  of  which  one  is 
worked  where  it  runs  around  18  inches  and  over  in  thickness.  The 
seams  are  shallow,  the  coal  is  high  in  ash  and  sulphur  but  lends  it- 
self readily  to  hand  picking.  A  little  anthracite  is  reported  from  Le- 
preau  in  St.  Johns  County. 


FIG.  no.  —  Coal  seam  (retouched)  in  sea  cliff  on  coast  of  Nova 
Scotia.     (Photo  by  H.  Ries.) 

Ontario.  —  There  is  a  small  area  of  about  10  square  miles  along 
the  lower  part  of  the  Moose  River/  south  of  James  Bay,  which  is 
underlain  by  lignite.  This  coal  was  formed  in  an  interglacial  period 
and  it  lies  between  two  beds  of  boulder  clay.  It  is  suitable  for  future 
briquetting  operations.  There  are  no  Carboniferous  rocks  in  Ontario 
and  Quebec.  The  formations  are  largely  pre-Cambrian,  except  for 
some  older  Palaeozoics  in  the  southern  part  of  Ontario  and  around 
James  Bay. 


ALBERTA  343 

Manitoba.  —  In  the  Tertiary  rocks  capping  a  hill  called  Turtle 
Mountain  and  in  adjacent  hills  along  the  International  Boundary 
there  are  some  seams-  of  lignite.  The  eastern  part  of  Manitoba  is 
covered  with  pre-Cambrian  rocks  and  the  western  portion  chiefly  by 
marine  Cretaceous. 

Saskatchewan.  —  The  coal  of  Saskatchewan  occurs  in  the  Ter- 
tiary and  Upper  Cretaceous  formations.  The  Tertiary  formations 
seem  to  correspond  to  the  Fort  Union  lacustrine  and  land-formation 
stage  of  the  Eocene  in  North  Dakota,  and  they  are  found  in  the  hilly 
country  in  the  southern  part  of  the  province.  The  strata  lie  prac- 
tically flat  except  for  a  syncline  under  the  Souris  River  Valley  and  the 
seams  outcrop  along  ravines  and  on  hillsides.  A  good  deal  of  coal  is 
mined  in  the  Souris  Valley  region  and  in  a  number  of  other  places, 
and  wagon  mines  are  common  as  many  of  the  western  farmers  dig 
their  own  coal.  The  Tertiary  coal  is  practically  all  lignite  and  the 
maximum  thickness  of  the  seams  is  about  20  feet.  The  Cretaceous 
coals  occur  in  the  Belly  River  formation  of  the  Upper  Cretaceous 
along  the  Saskatchewan  River,  in  the  western  part  of  the  province. 
The  coal  lies  from  200  to  300  feet  below  the  surface  and  there  are  at 
least  two  seams  about  4  feet  and  8  feet  thick  respectively.  They 
are  not  uniform  in  thickness  or  regular  in  distribution.  This  coal 
also  is  lignite.  A  little  lignite  occurs  in  the  Middle  Cretaceous  south 
of  Lac  la  Rouge. 

Alberta.  —  In  the  province  of  Alberta  coal  occurs  in  the  Kootenay 
series  of  the  Lower  Cretaceous;  in  the  Belly  River  series,  correspond- 
ing to  the  St.  Pierre  of  the  Montana  series  of  the  Upper  Cretaceous; 
and  in  the  fresh-water  deposits  of  the  Edmonton  formation,  corre- 
sponding to  the  Fort  Union  beds  of  the  Eocene. 

The  Kootenay  series,  regarded  as  lacustrine  and  terrestial  in  origin, 
contains  the  best  coals  of  Canada,  they  being  bituminous  to  an- 
thracite. It  lies  deeply  buried  beneath  the  younger  sediments  ex- 
cept where  it  is  brought  to  light  in  the  folds  along  the  foothills  or  in 
the  great  fault  blocks  of  the  Rocky  Mountains.  Its  thickness  varies 
from  200  to  about  3000  feet.  The  coal-bearing  area  in  Alberta  ex- 
tends from  tlre»  International  Boundary  northward  beyond  the  Atha- 
basca River  and  while  little  development  work  or  even  prospecting 
has  been  done  in  much  of  this  great  area,  several  very  important 
mining  districts  have  developed.  The  most  important  of  these  is  in 


344 


THE   COAL  FIELDS  OF  THE  WORLD— AMERICA 


the  region  of  Crowsnest  Pass  on  the  Crowsnest  branch  of  the  Can- 
adian Pacific  Railway.  Mines  occur  at  several  places  in  the  Blairmore- 
Frank  region.  A  half  dozen  seams  occur,  ranging  from  3  to  17  feet  in 
thickness.  It  was  at  Frank  that  the  famous  landslide  occurred  which 
carried  away  a  section  of  Turtle  Mountain.  It  destroyed  a  number 
of  houses  in  the  town,  killing  ninety-three  people,  and  it  buried 
the  railroad  through  the  valley,  (Fig.  in).  The  track  was  so  deeply 


M*    .  *»  . 


FIG.  in.  —  D6bris  from  the  landslide  at  Frank,  Alberta,  partly  covering 
the  town.     (Photo  by  E.  S.  Moore.) 

buried  that  a  new  line  was  constructed  over  the  debris  which  con- 
sisted chiefly  of  great  blocks  of  limestone.  The  lower  portions  of 
the  mountain  are  composed  largely  of  shales  and  coal  seams,  while 
the  upper  portion  contains  heavy  beds  of  limestone.  The  mining 
operations,  which  had  been  carried  well  through  the  mountain, 
apparently  disturbed  the  overlying  strata  and  a  large  crack  devel- 
oped which  caused  a  tremendous  mass  of  rock  to  break  away,  slide 
down  the  mountain  and  across  the  valley. 

In  the  Coleman  area  there  are  three  seams  as  much  as  8,  10  and  16 


ALBERTA 


345 


feet  in  thickness,  respectively,  within  a  thickness  of  300  feet  of  strata. 
In  the  Livingstone  basin  lying  a  short  distance  northward  from  the 
Blairmore-Frank  region,  there  are  in  Cat  Mountain  as  many  as  twenty- 
one  seams  with  a  total  of  about  125  feet  of  coal.  On  the  west  fork  of 
the  McLeod  River  southeast  of  Folding  Mountains  there  are  four  seams 


CROWSNEST   COAL   AREA 

SCALE  OF  MILES 


FIG.  112.  —  Map  of  the  Crowsnest  coal  area.     (After  D.  B.  Bowling.) 

in  the  Folding  Mountain  anticline  on  the  eastern  limb  and  they  vary 
from  2  feet  to  28  feet  in  thickness.  On  the  western  limb  a  combina- 
tion of  seams  forms  one  mass  as  much  as  50  feet  thick. 

In  the  Cascade  area  there  is  a  continuous  coal  field  extending  for 
about  90  miles  from  south  of  the  Kananaskis  River  northward  to  near 


346  THE   COAL   FIELDS  OF  THE  WORLD— AMERICA 

the  Saskatchewan  River.  This  is  a  great  fault  block  with  a  fault 
running  along  the  western  edge  of  the  coal  field.  In  some  portions 
there  are  between  15  and  20  seams  of  coal  with  a  maximum  aggregate 
thickness  of  nearly  100  feet.  Remnants  of  a  very  extensive  coal- 
bearing  area  are  found  along  the  Bow  River  and  there  are  mines  at 
Canmore.  At  Bankhead,  not  far  from  Banff,  semi-anthracite  and 
anthracite  are  mined,  and  mines  were  formerly  worked  at  Anthracite. 
These  beds  have  been  highly  squeezed.  Other  important  areas  in 
Alberta  are  the  Bighorn,  Brule  Lake,  Nikanassin,  Muskeg  River, 
Shunda  Creek,  Costigan,  and  Moose  Mountain  in  the  foothills  near 
Calgary.  In  Folding  Mountain  the  beds  are  highly  folded  so  that 
they  are  practically  vertical. 


FIG.  113.  —  Structure  section  through  the  Blairmore-Frank  region,  Alberta,  i, 
Devono-carboniferous;  2,  Lower  cretaceous  or  Jurassic  (Fernie  shales);  3,  Coal 
measures;  4,  Equivalent  of  flathead  beds;  5,  Volcanic  ash  and  agglomerates;  6, 
Upper  cretaceous  and  laramie;  3-6,  Cretaceous.  Scale  4  miles  =  i  inch.  (After 
D.  B.  Dowling,  Canadian  Geol.  Survey.) 

The  abundance  and  high  quality  of  the  coal  in  western  Alberta  and 
the  adjoining  portion  of  British  Columbia  make  this  region  the  most 
promising  coal-mining  region  of  Canada.  There  is  a  great  deal  of 
good  coking  coal. 

The  Belly  River  formation  underlies  about  16,000  square  miles  in 
eastern  Alberta.  The  best  coal  in  this  formation  is  being  mined  at 
Lethbridge.  The  coal  improves  as  the  mountains  are  approached. 
Around  Medicine  Hat  two  seams,  each  about  5  feet  thick,  are  exposed 
along  the  Bow  River.  In  the  vicinity  of  Calgary  the  Belly  River 
formation  is 'struck  at  depths  of  from  2560  to  2875  feet  and  the  coal 
varies  from  4  to  7  feet  in  thickness.  At  Edmonton  the  depth  is  about 
1400  feet  and  the  coal  about  6  feet  thick.  In  the  Peace  River  Valley 
there  is  some  coal  in  the  Dunvegan  series  supposed  to  be  equivalent 
to  this  formation.  There  is  much  coking  coal  in  the  Belly  River  for- 
mation. 


ALBERTA 


347 


The  Edmonton  (Eocene)  series  occurs  in  a  large  synclinal  basin 
which  runs  nearly  parallel  to  the  Rocky  Mountains  and  extends  over 
about  4  degrees  of  latitude.  The  dips  are  steep  on  the  western  and  low 
on  the  eastern  limb  of  the  basin  and  the  basin  flattens  out  to  the  north- 
westward. At  Calgary  there  is  a  seam  of  lignite  about  13  feet  thick 


FIG.  114.  —  Peaks  behind  Canmore,  Alberta.    About  two-thirds  of  mountain  face  is 
Palaeozoic  strata  thrust  over  folded  Mesozoic   coal  measures.     (Photo  by  H.  Ries.) 

under  cover  of  1800  feet  of  poorly  consolidated  sandstone  and  clay. 
On  the  North  Saskatchewan,  west  of  Edmonton,  a  25-foo.t  seam  out- 
crops and  on  the  Grand  Trunk  Pacific  Railway  line  at  the  Pembina 
River  crossing  it  splits  into  two  seams  each  10  feet  thick.  About 
500  feet  below  this  seam  several  smaller  seams  occur  over  several 


348  THE   COAL  FIELDS  OF  THE  WORLD— AMERICA 

thousand  square  miles  and  they  are  mined  at  Edmonton,  Tofield 
and  at  other  places  between  Edmonton  and  Calgary.  The  coal  varies 
from  lignite  in  the  northwestern  part  of  the  basin  to  a  subbituminous 
and  coking  coal  in  the  foothills  of  the  Rockies. 

British  Columbia.1  —  The  coal  deposits  of  this  province  are  grouped 
by  Dowling  under  the  five  following  heads:  Southern,  Central  and 
Northern  British  Columbia,  Vancouver  Island  and  Queen  Charlotte 
Islands.  In  the  Southern  district  is  located  the  Crowsnest  area  which 
is  a  basin  of  about  230  square  miles  around  which  lower  beds  have  been 
uplifted  and  then  eroded  on  a  large  scale  leaving  the  coal  field  as  an 
elevated  plateau.  The  coal  occurs  here,  as  elsewhere  in  the  Rocky 
Mountains,  in  the  Kootenay  series  of  the  Lower  Cretaceous  and 
most  of  the  better  seams  occur  in  the  lower  2000  feet.  It  is  said, 
however,  that  these  upper  seams  are  very  largely  cannel  or  other  high 
volatile  coals. 

The  following  is  a  tabulation  of  the  seams  in  this  area: 

At  Morrissey  23  seams  with  216  feet  of  coal  in  3676  feet  of  measures 
At  Fernie        23  seams  with  172  feet  of  coal  in  2250  feet  of  measures 
At  Sparwood  23  seams  with  173  feet  of  coal  in  2050  feet  of  lower  measures 
At  Sparwood  24  seams  with    43  feet  of  coal  in  2015  feet  of  upper  measures 

At  Corbin  a  seam  80  feet  thick  is  worked.  The  coal  is  in  places 
highly  faulted  and  folded  and  it  is  worked  from  tunnels.  The  coal- 
bearing  strata  occupy  a  basin  which  is  in  a  hill,  and  on  top  of  the  hill 
there  is  so  little  cover  that  the  coal,  which  is  here  125  feet  thick,  is 
stripped  and  mined  by  steam  shovels. 

The  Flathead  River  area  lying  about  12  miles  north  of  the  Inter- 
national boundary  gives  promise  of  being  a  very  important  field 
for  its  size.  It  is  probably  a  faulted  block  with  the  strata  dipping  only 
about  20°  and  exposing  four  seams  which  are  16,  20,  30  and  50  feet 
thick,  respectively.  The  Upper  Elk  River  area  north  of  the  Crows- 
nest  area  will  probably  be  an  important  field  as  there  are  as  many  as 
eighteen  seams  in  one  section  and  there  is  an  aggregate  of  182  feet  of 
coal  in  1200  feet  of  strata.  One  seam  reaches  31  feet  in  thickness. 
The  coal  in  this  area  as  in  the  others  mentioned  above  is  high-grade 
bituminous  coal  and  it  is  used  largely  for  coking. 

At  Princeton  on  the  Similkameen  River  there  is  a  small  basin  con- 

1  Coal  Fields  of  British  Columbia,  Compiled  by  D.  B.  Dowling,  Memoir  69.  Geol 
Survey,  Canadian  Department  of  Mines,  1915. 


BRITISH  COLUMBIA  349 

taining  lignite  of  Oligocene  age.  There  are  as  many  as  seventeen 
seams  in  one  section  and  the  thickness  varies  from  i  foot  to  18  feet. 
South  of  Tulameen  similar  lignite  of  Oligocene  age  occurs  with  two 
or  three  seams  from  1 2  to  20  feel  thick.  In  the  Nicola  and  Quilchena 
basins  there  are  also  Oligocene  deposits.  Several  collieries  have  been 
opened  near  the  mouth  of  Coldwater  Creek  in  the  Nicola  basin  and  in 
that  region  four  seams  running  from  5  to  12  feet  in  thickness  are  mined. 
The  coal  is  used  for  locomotives  as  it  is  of  better  grade  than  the  lig- 
nite in  the  other  regions.  The  basin  is  considerably  broken  by 
faults  and  it  has  been  overlain  by  basalt  flows. 

In  the  Central  British  Columbia  region  a  number  of  coal  deposits 
occur  but  many  of  them  have  not  been  proven  to  be  of  special  im- 
portance. In  the  valley  of  the  Bear  River  bituminous  coking  coal 
was  found  along  the  Grand  Trunk  Pacific  Railway  in  three  seams 
running  from  4  feet  to  9  feet  in  thickness.  It  is  of  Tertiary  age.  On 
the  southern  tributaries  of  the  Skeena  River  the  Lower  Cretaceous 
rocks  carry  a  few  seams  of  mineable  bituminous  coal.  In  the  Telka 
River  area  some  thick  seams  of  coal,  19,  24  and  13  feet  in  thickness 
occur.  The  coals  are  reported  to  be  of  coking  quality. 

Several  areas  of  coal-bearing  rocks  occur  in  the  Northern  British 
Columbia  district.  In  the  Groundhog  Mountain  area  on  the  head 
waters  of  the  Skeena,  semianthracite  coal  occurs  in  Lower  Cretaceous 
rocks  of  the  Skeena  series,  resting  on  Jurassic  volcanics.  The  area 
is  greatly  broken  by  faults.  In  the  Peace  River  district  there  is  a 
projection  of  the  coal  formations  described  for  Alberta.  Tertiary 
lignites  also  occur  on  the  Liard  and  Taku  rivers  but  the  deposits  are 
little  known. 

The  coal  seams  of  Vancouver  Island  are  of  Upper  Cretaceous  age, 
according  to  C.  H.  Clapp,  and  they  occur  in  the  Nanaimo  series  which 
is  supposed  to  be  largely  estuarine  in  origin  and  is  about  10,000  feet 
thick.  The  topographic  conditions  during  its  formation  were  not 
uniform  and  the  beds  in  many  cases  lack  persistency.  The  series  has 
in  places  been  greatly  folded  and  faulted.  The  coal  is  of  bituminous 
quality.  There  are  six  main  basins  as  follows:  Quatsino  Sound  at 
the  northern  end  of  the  island;  Suquash  on  the  east  coast;  Comox, 
Nanaimo  and  Cowichan,  all  on  the  Strait  of  Georgia;  and  the  Alberni 
in  the  central  part  of  the  island.  The  Suquash,  Comox  and  Nanaimo 
basins  contain  seams  which  are  being  worked.  In  the  Suquash 


350  THE   COAL   FIELDS   OF   THE   WORLD— AMERICA 

basin  the  beds  are  little  disturbed  and  regular.  The  coal  is  a  low 
carbon,  high  moisture,  bituminous  coal.  In  the  Comox  basin  the 
lower  seams  lie  over  an  irregular  bottom  and  are  quite  irregular  in 
thickness  and  distribution.  In  some  places  the  coal  is  broken  and 
coked  by  igneous  intrusions.  It  is  bituminous  and  coking  and  has 
the  highest  fuel  ratio  of  any  of  the  Vancouver  Island  coals.  In  the 
Nanaimo  field  there  are  many  faults  and  the  seams  vary  very  greatly 
in  thickness  and  quality  within  short  distances,  but  they  are  quite 
persistent  in  extent.  A  case  is  cited  by  Clapp  where  a  seam  varies, 
within  100  feet,  from  2  feet  of  dirty  slickensided  coal  to  30  feet  of 
clean  coal.  There  are  three  seams  with  an  aggregate  of  10  feet  of  coal 
which  is  a  high-volatile,  coking,  bituminous  variety.  This  basin 
has  produced  the  larger  part  of  the  coal  of  British  Columbia. 

The  coals  of  the  Queen  Charlotte  Islands  are  of  two  geological 
ages  —  Cretaceous  and  Tertiary,  supposedly  Miocene.  The  Creta- 
ceous coals  vary  from  high- volatile  bituminous  to  semianthracite  and 
the  Tertiary  are  subbituminous  coals  and  lignites,  some  of  the  latter 
of  very  woody  types.  Part  of  the  Cretaceous  coal  is  coking.  The 
semianthracite  is  unusually  high  in  water  and  much  of  it  is  high  in  ash. 
The  main  basin  lies  on  the  southern  end  of  Graham  Island  where  the 
shales  have  been  highly  folded  between  masses  of  crystalline  rocks. 
In  some  places  the  coal  is  greatly  crushed.  The  Tertiary  coals  are 
not  of  much  importance. 

Yukon  Territory.  —  Coal  has  been  mined  at  five  points  in  the 
Yukon:  Tantalus  Mine,  and  Five  Fingers  Mine  on  the  Yukon  River; 
on  Cliff  Creek;  on  Coal  Creek,  a  tributary  of  the  Yukon;  and  on  Coal 
Creek,  a  tributary  of  Rock  Creek.  According  to  the  conclusions  of  D. 
D.  Cairnes,  the  coals  are  Jura-Cretaceous  and  Tertiary  in  age.  The 
Tertiary  coals  are  upper  Eocene  and  they  are  lignites  with  con- 
siderable resin.  In  places  volcanic  rocks  are  associated  with 
the  soft  shales  and  clays  and  loosely  cemented  conglomerates  and 
sandstones. 

There  are  two  coal  horizons  in  the  Jura-Cretaceous  rocks,  the  upper 
being  the  Tantalus  conglomerates,  about  1000  feet  thick,  and  the 
lower  the  Laberge  series  about  3800  feet  in  thickness.  The  coal 
seams  occur  near  the  top  of  the  latter  series  which  consists  of  arkoses, 
graywackes,  sandstones,  tuffs,  shales  and  slates.  The  coal  is  bitumi- 
nous and  in  most  places  non-coking.  The  coal  of  the  lower  seam 


THE  ARCTIC  ISLANDS 


351 


when  washed  produces  commercial  coke.     Some  semianthracite  occurs 
in  the  Whitehorse  area. 

Northwest  Territories.  —  There  are  several  coal  basins  in  this 
region.  One  of  these  in  Tertiary  rocks,  occurs  in  the  Mackenzie 
River  valley  and  runs  a  short  distance  up  the  Bear  River  at  Fort  Nor- 
man. There  is  probably  a  lignite  area  running  south  up  the  valley 
of  the  Mackenzie  from  Fort  Norman  and  an  area  around  the  north- 
west side  of  Great  Bear  Lake.  Three  seams  have  been  reported  with 
a  maximum  of  about  16  feet  of  coal. 


FIG.  115.  —  The  Tantalus  coal  mine  on  the  Yukon  River.     (Photo  by  E.  S.  Moore.) 

Along  the  Peel  and  Horton  rivers  in  the  vicinity  of  the  Mackenzie 
delta  there  are  Cretaceous  rocks  carrying  thin  seams  of  coal  with  a 
maximum  thickness  of  4  feet.  Some  of  the  seams  have  been  on  fire 
in  the  past,  producing  reddened  outcrops  which  offer  striking  features 
to  the  traveler.  So  far  as  known  all  the  coal  in  the  Territories  is 
lignite. 

The  Arctic  Islands.  —  Very  little  accurate  information  regarding 
the  coal  deposits  on  the  Arctic  Islands  has  been  obtained  but  it  is 
known  that  coal  occurs  at  two  horizons,  in  the  Tertiary  and  in  the 
Lower  Carboniferous.  The  Tertiary  coals  are  lignites  and  the  older 


352  COAL  FIELDS  OF  THE  WORLD— AMERICA 

coals  are  bituminous.  It  is  estimated  that  some  6000  square  miles 
on  Banks  Island  and  the  Parry  Islands  is  underlain  with  Lower 
Carboniferous  coals.  Only  one  seam  has  been  found  but  it  is  said 
to  reach  a  maximum  of  50  feet  in  thickness.  Small  deposits  of  Ter- 
tiary coal  are  believed  to  exist  on  Ellsmere,  Baffin  and  Bylot  islands. 
On  Ellsmere  Island  a  seam  of  Tertiary  coal  25  feet  thick  has  been 
reported  from  Cape  Murchison.  Cannel  coal  and  oil  shale  have  been 
found  on  the  Parry  Islands. 

NEWFOUNDLAND 

Owing  to  the  prominence  of  the  large  and  well  developed  coal 
deposits  in  Nova  Scotia  little  attention  has  been  paid  to  the  Newfound- 
land deposits  which  are  not  so  extensive  nor  so  readily  mined  as  those 
in  Canada.  There  are,  however,  at  least  two  areas  of  Carboniferous 
rocks  which  carry  considerable  coal  in  Newfoundland.  One  area 
is  on  St.  George  Bay  and  the  other  is  about  100  miles  northeast  of  it 
in  the  Humber  River  valley.  In  the  former  area  there  are,  according 
to  J.  P.  Howley,  as  many  as  nine  seams  varying  in  thickness  from 
i  foot  to  9  feet.  The  beds  are  greatly  disturbed  and  many  of  the 
seams  are  of  small  extent. 

In  the  Humber  River  valley  the  strata  are  for  the  most  part  older 
than  the  Pennsylvanian  and  they  carry  oil  shales  and  material  re- 
sembling the  albertite  of  New  Brunswick.  There  are,  however,  in 
parts  of  the  district  small  areas  of  the  Coal  Measures  which  carry 
several  workable  seams  running  up  to  about  6  feet  in  thickness  and 
some  of  the  seams  are  greatly  folded  although  in  much  of  this  field 
the  strata  are  nearly  flat.  The  Newfoundland  coals  are  bituminous 
to  semibituminous  in  character. 

COAL  DEPOSITS  or  THE  UNITED  STATES 

PRODUCTION 

The  United  States  not  only  has  the  largest  deposits  of  coal  of  any 
country  in  the  world  but  she  is  also  developing  them  at  a  more  rapid 
rate  than  any  other  country.  A  preceding  table  (page  335)  shows 
the  relative  production  of  the  countries  of  the  world  and  the  following 
table  indicates  the  rank  of  the  various  states  of  the  Union  in  pro- 
duction and  the  value  of  the  coal  produced.  Pennsylvania  has  long 
been  the  chief  producer  in  the  country. 


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354 


THE   COAL  FIELDS  OF  THE  WORLD— AMERICA 


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co        oo" 


I   § 


ft! 


§    S 


S    3 


Total  bitumi 
Pennsylvania 
anthracite  .. 


•I 


T3 

I 

•a 

C8  ^ 

ill 

|3l 

-.11 


o  Cali 
b)  Inclu 
Mineral 


BITUMINOUS  AND  ANTHRACITE  COAL 
A    Indicates  anthracite  coal  Q  coking  coal 


Areas 

containing  workable 
coal  beds 


Areas  that  may  Areas  probably  containing 

contain  umrkable  Workable  coal  beds  under 

coal  beds  such  heauy  cover  as  not 

to  be  qvailable  at  present 


Areas 

containing  workath 
coal  beds 


PLATE  XII.— Map  of  the  coal-fields  of  the  United  States  (U.  S.  Geol.  Survey. 


•  UBBITUMINOUS  COAL 


UiGNITE 


Areas  that  may  Areas  probably  containing 

contain  workable  workable  coal  beds  under 

coal  beds  such  heavy  cover  as  not 

to  be  available  at  present 


I               I  I               I 

Areas  Areas  that  may 

containing  workaSEe  contain  workable 

lignite  beds  lignite  beds 


nted  by  permission  from  Rles1  Economic  Geology,  published  by  John  Wiley  &  Sons,  Inc.) 


DISTRIBUTION   BY   KINDS  OF   COAL  355 

DISTRIBUTION  BY  KINDS  OF  COAL 

The  Geological  Survey  has  adopted,  according  to  M.  R.  Campbell, 
the  following  divisions  in  classifying  the  coal  areas  of  the  country, 
(Plate  XII):  (i)  Coal  province  (2)  Coal  region  (3)  Coal  field  (4) 
Coal  district.  The  following  provinces  have  been  recognized:  (i) 
Eastern  province;  (2)  Interior  province;  (3)  Gulf  province;  (4) 
Northern  Great  Plains  province;  (5)  Rocky  Mountain  province; 
and  (6)  Pacific  Coast  province.  These  provinces  are  subdivided  into 
regions  as  follows:  The  Eastern  province  is  divided  into  (a)  The 
Anthracite  region  of  Pennsylvania;  (b)  The  Atlantic  Coast  region, 
including  the  Triassic  fields  of  Virginia  and  North  Carolina;  (c)  The 
Appalachian  region  extending  from  northern  Pennsylvania  into 
Alabama  and  embracing  also  parts  of  Ohio,  Maryland,  Virginia,  West 
Virginia,  Eastern  Kentucky,  Tennessee  and  Georgia.  The  Interior 
province  is  divided  into  (a)  the  Northern  region,  containing  only  the 
coal  field  of  Michigan;  (b)  The  Eastern  region  including  the  fields 
of  Illinois,  Indiana  and  Western  Kentucky;  (c)  The  Western  region 
including  the  coal  fields  of  Iowa,  Missouri,  Nebraska,  Kansas,  Ar- 
kansas and  Oklahoma  and  (d)  The  Southwestern  region,  in  Texas. 
The  Gulf  province  includes  (a)  The  Mississippian  region,  in  the 
east  and  (b)  The  Texas  region  to  the  west.  The  former  includes  the 
states  of  Louisiana,  Mississippi  and  Alabama  and  the  latter  Arkansas 
and  Texas. 

The  Northern  Great  Plains  province  includes  (a)  The  Fort  Union 
region  with  the  lignite  fields  of  North  Dakota,  South  Dakota,  eastern 
Montana  and  the  subbituminous  field  of  northeastern  Wyoming; 
(b)  The  Black  Hills  region  of  Wyoming;  (c)  The  Assinniboine  region 
in  Montana;  (d)  The  Judith  Basin  region  in  Montana;  (e)  The 
Denver  region  in  Colorado;  and  (/)  the  Raton  Mountain  region  of 
Colorado  and  New  Mexico. 

The  Rocky  Mountain  province  is  not  clearly  separated  from  the 
Great  Plains  province.  It  includes  (a)  The  Yellowstone  region  of 
Montana;  (b)  The  Bighorn  Basin  region  of  Wyoming;  (c)  The  Hams 
Fork  region  of  western  Wyoming;  (d)  The  Green  River  region  of 
southern  Wyoming;  (e)  The  Uinta  region  of  Utah  and  Colorado; 
(/)  The  San  Juan  River  region  of  Colorado  and  New  Mexico;  and 
(g)  The  southwestern  Utah  region. 
The  Pacific  Coast  province  is  not  divided  into  regions.  It  em- 


356  THE   COAL   FIELDS  OF  THE   WORLD— AMERICA 

braces  coal  fields  in  Calfornia,  Oregon  and  Washington.  It  is  the 
smallest  of  the  provinces. 

The  following  table,  prepared  by  Campbell  for  the  Twelfth  Inter- 
national Geological  Congress,  presents  the  areas  of  the  various  prov- 
inces, the  types  of  coal  in  each,  and  the  character  of  the  coal.  The 
total  production  of  each  state  to  the  end  of  1917  has  been  added  to 
show  the  extent  of  exhaustion  of  the  resources.  The  estimate  in- 
cludes all  seams  not  less  than  14  inches  thick  and  not  more  than 
3000  feet  below  the  surface.  A  detailed  description  of  the  classes  of 
coal  mentioned  in  this  table  is  found  in  Chapter  V  under  Classifi- 
cation of  Coals. 

The  total  estimated  tonnage  of  all  kinds  of  coal  for  the  United  States 
above  3000  feet  in  depth  is  3,225,394,300,000  metric  tons  or  about 
one-tenth  more  in  short  tons.  The  amount  produced  up  to  the 
end  of  1917  was  12,130,805,450  short  tons.  By  adding  approxi- 
mately 50  per  cent  of  this  amount  for  waste  in  mining  and  other 
operations  the  total  coal  exhausted  is  approximately  18,196,203,175 
short  tons.  This  is  almost  negligible  compared  with  the  coal  re- 
sources of  the  country,  being  slightly  more  than  one-half  of  one  per 
cent,  but  in  many  fields  the  output  represents  the  best  coal  from  the 
most  accessible  seams. 


*? 


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DISTRIBUTION   BY   KINDS  OF   COAL 

gftggJJ-fc  ..^oo  I 


357 


Coal  below 
surface  from 
3000  to  6000 
feet 


Anthracite 
and  Semi- 
anthracite 
al  (Class  A 


emibitu 
ous  coal 
i  Class 


Subbitumi- 
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i  Class  D) 


II 


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36 


IS     !f 


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358 


THE   COAL   FIELDS  OF  THE   WORLD— AMERICA 


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Yellowstone 
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Total 
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DISTRIBUTION   BY   KINDS  OF   COAL 

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360  THE   COAL  FIELDS   OF  THE  WORLD— AMERICA 

GEOLOGICAL  AGE  OF  THE  COAL-BEARING  FORMATIONS 

As  indicated  in  the  table  (page  338)  the  coal  seams  of  the  United 
States  range  from  Lower  Carboniferous  (Mississippian)  to  Miocene 
in  age.  The  eastern  part  of  the  country  in  a  general  way  may  be  said 
to  carry  the  Carboniferous,  Permian  and  Triassic  coals  and  the  west- 
ern and  Gulf  regions  the  Cretaceous  and  Tertiary  coals.  In  a  gen- 
eral way  it  may  be  said  also  that  the  coals  of  the  east  are  of  higher 
grade  than  those  of  the  west  because  all  the  lignite  and  most  of  the 
subbituminous  coal  lies  in  the  western  part  of  the  country  or  around 
the  Gulf  of  Mexico.  The  Carboniferous  system  is  the  great  coal  pro- 
ducer of  the  east  because  at  the  beginning  of  that  period  large  areas 
in  the  eastern  part  of  the  continent  had  but  recently  emerged  from 
beneath  the  sea.  There  were  excellent  conditions  for  the  develop- 
ment of  great  swamps  on  the  then  existing  low  lands  as  there  are 
along  the  coasts  of  Virginia  and  North  Carolina  today.  The  west- 
ern part  of  the  continent  was  still  largely  under  the  sea  at  that  time 
and  there  is  almost  no  Carboniferous  coal  in  that  part  of  the  country. 
The  age  of  the  coal  does  not  necessarily  determine  its  quality,  but, 
other  things  being  equal,  the  older  the  coal  usually  the  higher 
the  fixed  carbon  because  it  has  been  longer  subjected  to  pressure. 
There  is  much  excellent  coal  in  the  West  where  the  younger  forma- 
tions have  been  sufficiently  squeezed  to  devolatilize  it. 
The  geological  age  of  the  coal  according  to  provinces  is  as  follows: 
(a)  Eastern  province.  Semianthracite  occurs  in  the  Pocono  of 
the  Mississippian  in  Virginia,  in  two  small  basins  southeast  of  the 
main  field,  in  Frederick,  Pulaski  and  Montgomery  counties.  The 
other  coals  of  the  Eastern  province  all  occur  in  the  Pennsylvanian, 
or  Upper  Carboniferous,  except  those  in  the  Atlantic  Coast  region  and 
a  few  seams  in  the  Permian.  The  coals  in  the  Pennsylvanian  run 
through  the  Pottsville,  Allegheny,  Conemaugh  and  Monongahela 
series.  In  the  southeastern  portions  of  the  Appalachian  region  the 
coals  are  to  quite  a  large  extent  of  Pottsville  age.  For  example, 
those  of  the  famous  Pocahontas  field  of  Virginia  and  West  Virginia 
are  of  lower  Pottsville,  those  of  the  New  River  field  of  lower  and 
middle  Pottsville  and  much  of  the  coal  of  Alabama  and  Georgia  is  of 
Pottsville  age.  This  formation  carries  some  coal  throughout  the 
whole  Appalachian  region  but  outside  of  the  districts  mentioned  it 
is,  as  a  rule,  not  an  important  producer.  The  other  formations, 


GEOLOGICAL  AGE  OF  THE   COAL-BEARING  FORMATIONS       361 

especially  the  Allegheny  and  Monongahela,  carry  important  coals 
throughout  the  region  with  the  exception  that  the  latter  formation  is 
not  important  in  the  southern  part  of  the  field.  The  Permian  car- 
ries coal  in  Pennsylvania,  Ohio  and  Maryland.  In  the  Atlantic 
Coast  region  of  Virginia  and  North  Carolina  the  coal  is  Triassic  in 
age,  this  being  the  only  coal  of  that  age  in  the  country. 

(b)  Interior  province.     The  coals  are  all  Pennsylvanian,  the  most 
widespread  formations  being  the  Pottsville  and  the  Allegheny. 

(c)  Gulf  province.     The  coal  is  of  Upper  Cretaceous  and  Eocene 
age. 

(d)  Northern  Great  Plains  province.     The  coals  in  this  province 
range  from  the  Kootenay  of  the  Lower  Cretaceous,  around  the  Black 
Hills,  to  the  Fort  Union  of  the  Eocene,  in  which  the  bulk  of  the 
lignite  occurs.     There  is  much  difference  of  opinion  among  geologists 
as  to  whether  most  of  the  coal  occurs  in  the  Cretaceous  or  in  the 
Tertiary  as  the  dividing  line  between  the  two  systems  is  in  many  places 
not  distinct.     In  the  Dakotas  all  the  important  coal  seams,  which  are 
almost  entirely  lignite,  are  of  Eocene  age,  but  there  is  a  little  coal  in 
the  Lance  formation  of  the  Upper  Cretaceous.     In  Montana  the  coal 
runs  from  Jurassic  through  Lower  Cretaceous  and  Upper  Cretaceous 
to  Eocene,  very  little  of  it  being  Jurassic.     The  Wyoming  coals  are 
Lower  and  Upper  Cretaceous  and  Eocene  and  those  of  Colorado  are 
mostly  in  the  Montana  series  of  the  Upper  Cretaceous  with  important 
beds  in  the  Laramie  and  a  little  in  the  Dakota  series.     Those  of  New 
Mexico  are  also  of  Upper  Cretaceous,  (Montana)  age  with  the  excep- 
tion of  a  very  small  area  of  lower  Pennsylvanian. 

(e)  The  Rocky  Mountain  province  carries  coals  from  Lower  Cret- 
aceous to  Miocene  in  age.     In  addition  to  the  states  mentioned  under 
the  Northern  Great  Plains  province,  Arizona  contains  Upper  Cret- 
aceous coals;  those  of  Utah  are  mostly  in  the  Montana  and  Colorado 
series  of  the  Upper  Cretaceous,  and  some  lignite  occurs  in  the  Eocene. 
In  Idaho  the  coal  is  of  Upper  Cretaceous  and  Eocene  ages. 

(/)  In  the  Pacific  Coast  province  the  coals  are  chiefly  Eocene  in 
age  but  small  areas  are  Miocene. 


(362) 


PLATE  XIV.  —  Structure  section  through  the  Mahi 


m 


> 


and  Shenandoah  basins.    (By  courtesy  of  J.  Bevan.) 


PENNSYLVANIA  363 

THE  COAL  FIELDS  OF  THE  VARIOUS  STATES1 

Eastern  Province 

Pennsylvania.2  —  Pennsylvania  contains  the  anthracite  region  in 
the  east  and  the  bituminous  fields  in  the  west  and  north-central  parts 
of  the  state.  These  two  areas  were  originally  connected  but  they  have 
been  separated  by  erosion.  The  strata  in  the  bituminous  fields  are 
as  a  rule  but  slightly  folded  and  the  faults,  although  numerous  in 
some  districts,  are  not  of  great  throw,  while  in  the  anthracite  region 
the  strata  are  characteristically  highly  folded  and  there  are  extensive 
thrust  faults  which  complicate  the  mining  operations.  There  are 
some  anthracite  beds  which  lie  practically  flat  for  considerable  dis- 
tances. Such  are,  for  example,  some  of  those  in  the  Northern  basin 
around  Scranton  and  Wilkes-Barre.  These  have,  nevertheless,  been 
subjected  to  great  pressure  but  the  strata  have  resisted  buckling  and 
the  pressure  has  been  transmitted  to  the  coal  seam  changing  the  coal 
to  anthracite. 

Anthracite  region:  In  the  anthracite  region  the  coal  lies  almost 
entirely  in  the  synclines  as  it  has  been  protected  from  erosion  by  the 
Pottsville  conglomerate,  or  as  it  is  often  called,  Millstone  grit,  and  the 
Pocono  sandstones.  These  formations  are  brought  up  in  the  anticlines 
between  the  basins  and  between  these  formations  the  red  Mauch 
Chunk  shale  and  sandstone  makes  a  distinct  horizon-marker  and 
indicates  the  lower  limit  of  all  coal.  Usually  the  Pottsville  conglom- 
erate marks  the  base  but  a  few  seams  have  been  found  in  it.  Some 
of  the  synclines  are  probably  of  great  depth;  over  4000  feet,  in  the 
Southern  field.  Mining  has  not  so  far  been  carried  beyond  2200  feet, 
with  the  deepest  shaft  only  1850  feet,  but  it  must  be  in  the  future. 
The  region  is  usually  divided  into  the  Northern,  Eastern-middle, 
Southern  and  Western-middle  fields  and  these  fields  contain  the 
following  districts.  The  Northern  includes  Carbondale,  Scranton, 
Pittston,  Wilkes-Barre,  Plymouth,  Kingston  and  Nanticoke,  these 
making  up  the  Wyoming  trade  region.  The  Eastern-middle  field  in- 

1  For  special  comprehensive  reports  see:    22nd  Annual  Report,  U.  S.  Geol.  Survey, 
Part  III,  1902;  The  Coal  Catalog,  E.  N.  Zern,  Editor,  Keystone  Consolidated  Publishing 
Co.,  Pittsburgh,  1918;  The  Coal  Fields  of  the  United  States,  with  map,  by  M.  R.  Campbell, 
U.  S.  Geol.  Survey;  Coal,  by  E.  W.  Parker,  Mineral  Resources  of  the  United  States,  1910. 

2  Second  Geological  Survey  of  Pennsylvania;    County  Reports  and  Geologic  and 
Topographic  Survey  Commission  reports.    Also  22nd  Annual  Report,  U.  S.  Geol.  Survey, 
The  Pennsylvania  Anthracite  Coal  Field  by  H.  H.  Stoek. 


364  THE   COAL  FIELDS  OF  THE  WORLD— AMERICA 

eludes  the  Green  Mountain,  Black  Creek,  Hazleton,  Beaver  Meadow, 
and  Panther  Creek  districts,  these  making  up  the  Lehigh  trade  region. 
The  Southern  field  includes  the  East  Schuylkill,  West  Schuylkill, 
Lorberry  and  Lykens  Valley  districts,  while  the  Western-middle  field 
embraces  the  local  districts  of  East  Mahanoy,  West  Mahanoy  and 
Shamokin.  The  last  two  fields  are  comprised  in  the  Schuylkill  trade 
region. 

The  structure  of  the  region  is  illustrated  by  the  accompanying  sec- 
tions (Pis.  XIII  and  XIV)  and  the  names  of  the  seams  and  their 
relations  to  one  another  are  also  indicated.  The  anticlines  lie  in  a 
general  direction  of  about  N.  70°  E.  and  as  a  rule  the  folds  are  steeper 
on  the  northwestern  side  of  the  anticline  than  on  the  opposite  side 
since  the  thrusts  producing  them  came  from  the  southeast.  The 
thickest  seam  is  the  Mammoth  which  reaches  50  to  60  feet  of  com- 
paratively clean  coal  and  in  some  places  is  doubled  by  folding  so  that 
over  100  feet  of  coal  occurs  in  a  stripping.  Since  the  cover  over  this 
and  some  of  the  other  seams  is  so  thin  much  coal  is  mined  by  stripping 
off  the  cover  and  digging  the  coal  with  steam  shovels.  The  depth  of 
the  cover  removed  varies  from  almost  nothing  to  90  feet,  although  one 
stripping  will  reach  almost  200  feet  in  depth  under  exceptional 
conditions.  This  is  at  Locust  Mountain. 

The  best-known  seams  in  the  various  fields  are  as  follows:  In  the 
Southern  field  there  are  the  six  Lykens  Valley  seams  in  the  Potts- 
ville  conglomerate,  No.  VI  being  the  lowest,  and  three  of  these  beds 
are  found  also  in  the  Western-middle  field.  They  vary  from  thin  un- 
workable seams  up  to  about  n  feet  in  the  Western-middle  field. 
There  are  no  workable  seams  in  the  Pottsville  in  the  other  two  fields. 

The  lowest  bed  in  the  Coal  Measures  proper  is  the  Buck  Mountain 
bed  of  the  Southern,  the  Western-middle  and  Eastern-middle  fields. 
This  bed  is  thickest  in  the  Western-middle  field  and  it  probably 
corresponds  to  the  lowest  split  of  the  lowest  Red  Ash  bed  in  the 
Northern  field.  It  runs  between  3  and  19  feet  in  thickness.  Be- 
tween the  Buck  Mountain  and  Mammoth  seams  in  the  Southern 
field  there  is  the  Skidmore  bed;  in  the  Western-middle  field  there 
are  the  Seven-foot  and  Skidmore  beds  and  in  the  Eastern-middle 
field  the  Gamma  bed,  the  Wharton  bed  and  the  Parlor  bed. 

In  the  Northern  field  the  lowest  workable  beds  are  the  three  Red 
Ash  or  Dunmore  beds,  also  known  as  the  Powder  Mill  and  Clifford 


PENNSYLVANIA  365 

beds.  Above  the  Dunmore  beds  lie  the  Ross  or  Clark  seam,  and  the 
Twin  beds,  followed  by  the  two  splits  of  the  seam  known  as  the 
Mammoth  in  the  other  fields.  In  this  field  this  seam  is  known  as 
the  Baltimore,  Pittston,  Fourteen-foot,  Big  Bed  or  Grassy  Island  bed. 
Above  this  big  seam  lie  the  Rock  bed  and  the  Diamond  bed,  each 
about  3  feet  thick,  followed  by  the  Hillman  or  Olyphant  No.  I,  running 
up  to  about  15  feet  in  thickness.  Above  this  seam  is  the  Kidney, 
Diamond  or  Olyphant  No.  II  which  probably  corresponds  to  the 
Diamond  beds  of  the  southern  fields.  It  is  about  5  feet  thick  in  this 
field.  The  Abbott  and  Snake  Island  beds  lie  above  it. 

In  the  Eastern-middle  field  the  Mammoth  bed  which  is  here 
around  58  feet  thick  is  the  highest  bed  of  importance  and  it  is  stripped 
a  great  deal.  In  the  Western-middle  field  there  are  the  Holmes 
bed,  the  Primrose  bed,  the  Orchard  beds,  the  Diamond  beds  and 
the  Tracy  beds,  lying  above  the  Mammoth  seam  which  is  here 
about  60  feet  thick. 

In  the  Southern  field  the  Mammoth  seam  has  a  number  of  splits 
making  up  a  total  of  about  1 20  feet  of  coal  and  partings.  The  seams 
lying  above  the  Mammoth  bed  are  practically  the  same  as  those 
just  mentioned  for  the  Western-middle  field  with  the  addition  of  the 
Clinton  beds.  About  twenty  different  beds  have  been  worked  in 
this  field. 

It  has  been  estimated  that  over  80  per  cent  of  the  coal  in  the  Wy- 
oming basin  and  approximately  75  per  cent  of  that  in  the  other 
fields  is  marketable.  The  Pennsylvanian  rocks  are  very  thick  in 
the  Southern  field,  the  Pottsville  conglomerate  varying  from  noo  to 
1475  feet  in  thickness  and  the  other  formations  making  up  2500  feet 
more.  In  the  Western-middle  field  about  1200  feet  of  measures 
remains,  and  in  the  Northern  field  a  maximum  of  2200  feet  is  found 
in  the  deep  basin  between  Nanticoke  and  Wilkes-Barre.  The  aver- 
age thickness  for  the  Pottsville  conglomerate  and  the  Coal  Measures 
respectively,  in  the  various  fields  is  placed  at  the  following  figures: 
Northern  field  225  and  1800  feet;  Western-middle  850  and  1000 
feet;  Eastern-middle  300  and  700  feet,  and  Southern  1200  and  2500 
feet. 

An  interesting  feature  in  the  Northern  field  is  the  buried  valley 
between  Pittston  and  Nanticoke  in  which  a  large  stream  flowed 
before  the  glacier  passed  over  the  region.  When  the  glacier  pushed 


•03  a 


nojnosq; 


I 


<    3 


I 


0< 


(366) 


PENNSYLVANIA 


367 


across  the  valley  in  the  Pleistocene  epoch  the  valley  was  filled  up 
and  since  the  glacier  melted  away  the  Susquehanna  River  has  made  a 
new  channel  for  itself.  It  has  also  been  suggested  that  this  valley 
may  have  been  caused  by  glacial  erosion.  Since  this  pre-glacial 
valley  is  filled  with  debris  which  holds  much  more  water  than  the 
solid  rock,  it  is  naturally  a  menace  in  mining  operations  and  it  has 
been  pretty  carefully  mapped  out. 


300- 


= 


Homewood  Sandstone 


Upper  Mercer  Coal 


20°-  -ZJ^I^I         Lower  Mercer  Coal 


200- 


100- 


. 


>    Conoqueneasing 


Sharon  Coal 

Sharon  Conglomerate 


FIG.  117.  —  Section  of  the  Pottsville 
in  Mercer  County,  Pa.  (After  I.  C. 
White,  U.  S.  Geol.  Survey.) 


Upper  Free  port  Coal  (E) 


Lower  Freeport  Coal  ( D  ) 


Freeport  Sandstone 

Upper  Kittanning  Coal  (C') 
Johnstown  Cement 


Middle  Kittanning  Coal  (C) 

Lower  Kittanning  Coal ( B) 

Ferriferous  Limestone 
Clarion  Coal  (A') 

BrookvilleCoal(A) 


FIG.  118.  —  Columnar  section  through 
the  Allegheny  formation  on  the  Alle- 
gheny River,  Armstrong  County,  Pa. 
(After  D.  White,  U.  S.  Geol.  Survey.) 


Pennsylvania  produces  almost  all  the  anthracite  mined  —  con- 
siderably over  99  per  cent  —  in  the  country.  Anthracite  was  dis- 
covered by  the  earliest  settlers  about  1762  and  used  by  smiths  and 
for  local  purposes  for  a  number  of  years  before  active  mining  began. 
The  records  of  shipments  begin  about  1805,  but  coal  is  said  to  have 
been  shipped  during  the  Revolutionary  War.  At  first  the  people 
in  the  towns  would  have  nothing  to  do  with  it  as  they  were  skep- 
tical regarding  its  value  as  a  fuel. 

The  Bernice  field  of  Sullivan  County  is  regarded  by  some  as  part  of 


368 


Feetr 


£ittle  Pittsburgh  Coal 


Connellsville  Sandstone 


Morgantown  Sandstone 


11—  -.T-_rJ    "Elk  Lick  Coal 


Crinoidal  Coal 


100- 


THE   COAL  FIELDS   OF  THE  WORLD— AMERICA 

the  anthracite  region  and  the  coal  is  put 
on  the  market  as  anthracite  although  it 
is  more  strictly  semianthracite.  It  marks 
the  transition  from  the  anthracite  region 
to  the  bituminous  fields  farther  west. 

Bituminous  region:1  The  bituminous 
fields  of  the  state  cover  14,200  square 
miles  and  while  the  southeastern  border 
of  the  area  has  suffered  a  good  deal  of 
compression  where  the  intensive  folding 
found  farther  east  dies  out,  the  beds  for 
the  most  part  have  gentle  dips  and  the 
coal  occurs  in  a  large  number  of  roughly 
parallel  synclinal  basins.  The  Broad  top 
field  in  Huntingdon  and  Bedford  counties 
is  a  remnant  of  the  Coal  Measures  folded 
down  into  the  mountains  in  that  lo- 
cality and  it  is  more  disturbed  than  most 
of  the  other  bituminous  fields.  Owing 
to  the  greater  amount  of  folding  which 
the  eastern  portion  of  the  bituminous 
area  has  suffered,  much  of  the  coal  is 
semibituminous  in  character  and  the 
Clearfield  district  is  noted  for  its  "  Smoke- 
less coal  "  of  this  variety. 

The  coals  occur  chiefly  in  the  Alle- 
gheny and  Monongahela  series  of  the 
Coal  Measures,  between  40  and  50  per 
cent  of  the  coal  mined  coming  from  the 
former  series.  The  Pottsville  (Fig.  117) 
contains  the  Sharon  and  Mercer  coals 
mined  in  restricted  areas.  The  Allegheny 
(Fig.  1 1 8)  is  about  300  feet  thick  on  the 
average  and  contains  the  Brookville,  or 

1  White,  D.,  and  Campbell,  M.  R.,  The  bitumi- 
nous coal  fields  of  Pennsylvania.  22nd  Annual  Rept. 
U.  S.  Geol.  Survey,  Pt.  Ill,  1902.  Also  White, 
U.  S.  Geol.  Survey,  Bull.  65. 


Bakerstown  Coal 


,Masontown  Coal 


Mahoning 


FIG.  119  —  Columnar  section 
through  the  Conemaugh  forma- 
tion on  Dunbar  Creek,  Fayette 
County,  Pa.  (After  I.  C. 
White,  U.  S.  Geol.  Survey.) 


PENNSYLVANIA 


369 


Waynesburg  Coal 


300- 


200- 


Uniontown  Coal 


100- 


Sewickley  Coal 


A  coal,  the  Clarion  or  A1,  the  Lower  Kit  tanning  or  B,  the  Middle 
Kittanning  or  C,  the  Upper  Kittanning  or  C1,  the  Lower  Freeport 
or  D  and  the  Upper  Freeport  or  E.  The  Brookville  coal  is 
worked  in  many  places  in  the  eastern  counties  of  the  bituminous 
fields  and  the  Clarion  coal  is  of  workable  thickness  in  numerous  lo- 
calities. The  Lower  Kittanning  is  usually  Feet 
less  than  4  feet  thick  but  it  is  uniform  in 
distribution  and  character.  It  is  also  known 
as  the  Miller  seam.  It  is  a  valuable  coal 
in  at  least  eleven  counties.  The  Upper 
Kittanning  is  characterized  by  a  large 
amount  of  cannel  coal  in  Beaver  and  Clear- 
field  counties.  The  Middle  Kittanning  is 
not  relatively  important  as  it  is  thin  and 
in  many  places  dirty.  The  Upper  and 
Lower  seams  are  well  known  for  coking, 
domestic,  gas-producing  and  other  pur- 
poses. The  lower  Freeport  or  Moshannon 
seam  is  a  well-known  seam,  especially  in 
Clearfield,  Jefferson,  Indiana,  Cambria  and 
Center  counties.  This  coal  is  adapted  to 
almost  all  varieties  of  uses.  The  Upper 
Freeport  extends  over  a  large  area  but  it 
varies  greatly  in  thickness  and  quality. 

The  Conemaugh  series  (Fig.  119)  carries 
several  seams  such  as  the  Berlin,  Bakers- 
town  and  Coleman  but  they  are  compara- 
tively unimportant. 

The  Monongahela  series  (Fig.  120)  con- 
tains the  famous  Pittsburgh  seam  and  the 
Redstone,  Sewickley  and  Waynesburg  seams.  The  former  seam 
occurs  in  the  southwestern  portion  of  the  state  in  Greene, 
Washington,  Westmoreland,  Fayette,  Allegheny,  Somerset  and  In- 
diana counties.  It  runs  from  4  to  9  feet  in  thickness  and  averages 
about  7  feet  over  an  area  of  between  2000  and  2500  square  miles. 
The  coal  of  this  seam  is  excellent  for  a  great  variety  of  uses.  It  has 
been  the  famous  coking  coal  of  the  Connellsville  district,  and  West- 
moreland County  furnishes  one  of  the  best  of  gas  coals  from  this  seam. 


..Redstone  Coal 


Pittsburgh  Coal 


FIG.  1 20.  —  Columnar  section 
of  the  Monongahela  forma- 
tion in  Fayette  County,  Pa. 
(After  Stevenson,  U.  S.  Geol. 
Survey.) 


370 


THE   COAL   FIELDS  OF  THE  WORLD— AMERICA 


The  Redstone  seam  is  about  3 J  feet  thick.     It  is  mined  in  a  number 
of  places  in  the  southwestern  counties,  but  on  the  whole  it  is  not  very 

important.  The  Waynesburg  seam  is 
mined  in  Westmoreland,  Washington  and 
Greene  counties.  It  is  about  3  feet  thick 
on  the  average  but  locally  it  runs  6  feet, 
and  in  places  it  is  a  block  coal.  The  coal 
is  frequently  bony. 

The  Dunkard  series  of  the  Permian 
system  carries  the  Washington  seam  which 
is  worked  to  some  extent  in  Washington 
and  Greene  Counties.  It  may  reach  10 
feet  in  thickness  but,  like  the  Waynesburg 
seam,  it  carries  much  rock. 

Rhode  Island.1  —  The  coal  in  this  state 
is  interesting  chiefly  because  of  the  fact 
that  it  has  been  so  squeezed  and  broken  that 
some  of  it  has  been  turned  into  graphite, 
and  therefore  does  not  burn.  The  propor- 
tion of  fixed  carbon  is  so  high  compared 
with  the  volatile  matter  that  combustion 
will  not  take  place  in  some  of  the  coal.  The 
coal  is  also  very  high  in  ash,  much  of  it 
running  30  per  cent  or  more.  It  has  been 
mined  intermittently. 

Ohio.2  —  Many  of  the  seams  mined  in 
southwestern  Pennsylvania  continue  into 
Ohio.  They  are  all  bituminous.  In  the 
Pottsville  formation  (Fig.  122)  there  are  in 
ascending  order,  Sharon,  or  No.  i,  the 
block  coal;  Quakertown  or  No.  2;  and 

ru,  ^"olumnar  section  Lower  Mercer   or   No.    3.     Of    these    the 
through  the  Dunkard  forma-  Sharon,  which  is  about  3  feet  thick,  is  the 

tion  in  Greene  County,  Pa.    on}y  one  of  much   importance   although  the 
(After  Stevenson,  U.S.  Geol.  mjned    ^    certa;n    ^       The 

Survey.) 

Sharon  has  been  mined  in  limited  areas,  as 

1  Ashley,  G.  H.,  Rhode  Island  Coal.    U.  S.  Geol.  Survey,  Bull.  615,  1915. 

2  Bownocker,  J.  A.,  The  coal  fields  of  Ohio,  with  map.     U.  S.  Geol.  Survey,  Prof. 
Paper  loo-B,  1917.    Also,  Bull.  9,  Fourth  series,  Ohio  Geol.  Survey,  1908. 


OHIO  371 

around  Massillon  and  Jackson.  This  coal  is  largely  exhausted. 
It  is  characterized  by  coatings  of  calcium  carbonate  on  the  joints, 
known  as  "  white  cap."  The  sulphur  is  very  low  and  the  coal  has 
been  used  raw  in  the  blast  furnaces  in  making  pig  iron.  The 
Quakertown  bed,  also  known  as  the  Wellston  or  Jackson  Hill  bed, 
supplies  good  coal  for  domestic  and  steam  purposes,  and  in  Jackson 
County  where  it  is  mined  most  it  runs  about  4  feet  in  thickness. 
The  Lower  Mercer,  or  No.  3  and  the  Upper  Mercer  or  No.  30,  are 
unimportant.  They  are  characterized  by  lying  und^  thin  lime- 
stones which  go  by  the  same  name.  The  Upper  Mercer  is  also 
known  as  the  Bedford  cannel  and  in  Coshocton  County  it  reaches  a 
thickness  of  about  9  feet  of  which  5  feet  is  cannel. 

The  Allegheny  series  contains  the  most  widely  extended  and  best 
beds  of  the  state.  The  seams  in  ascending  order  are  the  Brookville 
or  No.  4,  the  Clarion  or  No.  40,  the  Lower  Kittanning  or  No.  5,  the 
Middle  Kittanning  or  No.  6,  the  Lower  Freeport  or  No.  6a  and  the 
Upper  Freeport  or  No.  7.  The  Brookville  seam  runs  from  2  to  4  feet 
in  thickness  and  it  is  not  extensively  mined  as  it  is  impure  and  thin 
over  large  areas.  The  Clarion  bed  lies  under  the  Vanport,  or  Ferrif- 
erous limestone,  which  is  a  good  horizon-marker.  It  is  of  compara- 
tively little  value.  The  Lower  Kittanning  is  not  of  great  impor- 
tance but  it  is  mined  and  a  very  important  bed  of  clay  lies  beneath  it. 
The  Middle  Kittanning  is  regarded  as  one  of  the  most  important  in 
Ohio.  It  usually  runs  around  3  to  4  feet  in  thickness;  it  is  high  in 
sulphur  in  many  places  but  is  widely  extended.  In  the  Hocking 
Valley  field  what  is  known  as  the  Jumbo  "  fault  "  causes  much  diffi- 
culty in  mining.  It  is  not  a  fault  but  an  old  "  cut-out  "  where  a 
stream  has  washed  away  the  vegetal  matter  and  deposited  sand  and 
mud  in  its  place.  The  Lower  Freeport  is  of  little  commercial  im- 
portance except  around  Steubenville,  while  the  Upper  Freeport  is  a 
very  important  seam.  The  coal  breaks  down  readily  and  is  not 
suitable  for  transportation  but  it  is  a  good  steaming  fuel.  Its  maxi- 
mum thickness  is  about  7  feet.  Lying  between  the  Upper  Freeport 
and  the  Pittsburgh  bed  is  the  Conemaugh  series,  about  350  to  500 
feet  thick.  It  contains  the  Mahoning,  Mason  and  Anderson  seams, 
the  latter  being  equivalent  to  the  Bakerstown  of  Pennsylvania,  but 
they  are  thin  and  little  worked. 

The  Monongahela,  or  Upper  Productive  Measures,  contains  three 


372  THE   COAL  FIELDS  OF  THE   WORLD— AMERICA 

seams  of  importance:  The  Pittsburgh  or  No.  8  at  the  base;  the  Red- 
stone or  Pomeroy,  or  No.  8a;  and  Meigs  or  No.  9.  The  Pittsburgh 
is  not  as  extensive  or  of  as  good  quality  as  the  Middle  Kit  tanning.  It 
occurs  in  the  three  fields,  Belmont  County,  Federal  Creek  and  Swan 
Creek.  The  coal  is  used  mostly  for  steam  and  domestic  purposes. 
It  runs  about  6  feet  in  thickness  with  several  clay  partings  in  many 
places,  and  thin  limestones  occur  in  the  shales  of  the  roof.  In  some 
areas,  as  in  Jefferson  County,  the  coal  is  mined  with  steam  shovels. 
The  Pomeroy  was  for  years  regarded  as  the  Pittsburgh  bed  of  Penn- 
sylvania but  it  is  now  known  to  be  the  equivalent  of  the  Redstone. 
It  runs  from  2  to  5  feet  in  thickness  and  is  high  in  ash.  The  Meigs 
Creek  is  an  important  bed  but  in  many  places  it  is  irregular.  It  is 
the  equivalent  of  the  Sewickley  seam  of  Pennsylvania.  The  coal  is 
used  mostly  for  steam  and  domestic  purposes.  It  is  like  many  of 
the  Ohio  coals  in  being  high  in  sulphur,  and  bands  of  pyrite  frequently 
occur.  In  the  Dunkard  group  of  the  Permian  there  are  several  thin 
seams  but  they  are  not  of  importance. 

Maryland.1  —  The  coals  of  Maryland  occur  in  the  following  five 
basins:  Georges  Creek,  Upper  Potomac,  Castleman,  Upper  Youghio- 
gheny  and  Lower  Youghiogheny,  all  confined  to  Allegheny  and 
Garrett  counties.  The  Georges  Creek  basin  is  the  most  prominent 
producer  with  most  of  the  remaining  coal  coming  from  the  Potomac 
basin.  The  coals  are  mostly  semibituminous.  The  following  seams 
are  recognized:  Brookville,  Clarion,  Lower  Kittanning,  Upper  Kittan- 
ning,  Lower  Freeport  and  Upper  Freeport,  in  the  Allegheny  series. 
Those  of  the  Pottsville  are  unimportant.  In  the  Conemaugh  the 
Bakerstown  seam  occurs  and  is  of  some  importance.  The  Mononga- 
hela  carries  the  Pittsburgh  seam  and  the  Upper  Sewickley,  also  known 
as  the  Gas  coal.  The  Pittsburgh  seam  or  "  Big  Vein  "  has  been  the 
main  source  of  the  coal  of  the  state  but  the  other  seams  are  being  devel- 
oped more  and  more  in  recent  years.  This  seam  runs  about  8  feet 
in  thickness  although  in  the  southern  part  of  the  field  it  reaches  14 
feet.  The  coal  is  massive  and  breaks  down  in  large  blocks.  It  fur- 
nishes a  famous  bunkering  and  steaming  coal  and  can  be  coked,  but 
it  is  not  used  to  any  extent  for  the  latter  purpose. 

West  Virginia.2  —  Many  of  the  coal  seams  of  Pennsylvania,  Ohio 

1  Clark,  W.  B.,  Maryland  Geol.  Survey,  Vol.  V,  1905. 

*  White,  West  Virginia  Geol.  Survey,  Vol.  II,  1903  and  Bull.  2,  1911. 


Shale 

Coal  No.  7  a 
Fire  clay 

Sandstone  andjshale      |5si5 


Coal  No.  7 
Fire  clay 
Limestone 


Gray  shale 

Buff  limestone 
Black  band  iron  ore 
Fire  clay 
Limestone 
Coal  No,  6  b 

Shale  and  limestone 


Coal  No.  6  i 
Fire  clay 


E2~==J  0-50 


0-50 


Gray  or  black  shale      |=f=^E-=|  5-50 

Coal  No.  6 
Fire  clay 
Limestone 

Gray  or  black  shale       |E™E:^=| 

Coal  No.  5 
Fire  clay 

Shale  and  sandstone     fe~t 


Limestone 
Coal 

Fire  clay 
Sandstone 
Coal  No.  4 

Shale  and  sandstone 


Coal  No.  3  b 
Shale  and  sandstone 
Coal  No.  3  a 
Limestone  with  iron  oi 

Fire  clay  5-15 

Shale  and  sandstone 


Coal  No.  2 
Fire  clay 

Shale 


Sandstone 


Gray  shale 

Coal  No.  1 
Fire  clay 


Conglomerate 


mm 

mm 


540 


Grof. 

Stripe  vein 
Brush  Creek 


Mahoning 

f  Upper  Freeport 
I  Cambridge 
]  Big  Vein 
I  Waterloo 

StillwelHoften 
conglomerate) 


Lower  Freeport 
Hatcher 
Steubenville 
Whaa 


Upper  Ktttanniiig 
(not  mined.in 
Ohio) 


(Hocking  Valley 
Straitsville 
Middle  Kittanning 
Sheridan 


Mineral-Point 
Lower  Kittanning 
Leetonia 
New  Castle 


Gray  ferriferous; 
Putnam  Hill. 
Upper  Clarion 


Brookeville 
f  Homewood 
\  Piedmont 

Tionesta 
(  Bruce 

\  Upper  Mercer 
(  Lower  Mercer 
\  Flint  Ridge  canne 

Upper  Massillon 

f  Wellston 
1   Quaker.tow.n 


Lower  Massillon 


{Brier 
Massil 
Jacksc 


Hill 

Massillon 
Jackson  Shaft 


STRATA 


SECTION  FEET 


Limestone 
Sandstone 
Coal  No.  13 

Stwidstoiu*  andLsh.a.1© 
CoalNoU2 


Limestone 


Black  shale 
Coal  No.  8 
Fire  clay 
Limestone 


30-70 


U-30 


Shale  and  sandstone      pE^^'S  110 
t-t^l^&l 


Shale 

Crinoidal  limestone 

Shale 

Coal  NO.  7  b 

Fire  clay 


Shale  and.  sandstone 


Shale 

Coal  No.  7  a. 

Fire  clay 


LOCAL  NAME 


Macksbure 
Waynesburg 


Meig  Creek 
Sewickley 


Redstone  in 
Pennsylvania 


Pittsburgh 


Norwich 
Patriot 


f  Grof. 
<  Stripe  vein 
Brush  Creek* 


FIG.  122.  —  Columnar  section  of  the  Carboniferous  formations  in  Ohio. 
Hazeltine,  U.  S.  Geol.  Survey). 


(After 
(373) 


374  THE    COAL   FIELDS   OF   THE  WORLD— AMERICA 

and  Maryland  extend  into  West  Virginia,  the  main  one  being  the 
Pittsburgh  bed.  This  state  is  the  second  most  important  producer 
in  the  Union  and  her  production  is  increasing  rapidly.  The  main 
fields  of  West  Virginia  are  the  Fairmont  or  Clarksburg,  the  Piedmont 
or  Elk  Garden  in  the  northern  part  of  the  state,  and  the  New  River, 
Kanawha  and  Pocahontas  fields  in  the  southern  part.  The  Piedmont 
field  is  a  narrow  field  lying  in  the  Potomac  basin  to  the  east  of  the 
others  and  it  carries  semibituminous  or  "  smokeless  "  coal  in  the 
following  well-known  veins:  Pittsburgh,  or  "  Big  Vein,"  Thomas, 
or  Upper  Freeport,  and  Davis,  probably  Upper  Kittanning.  The 
Pittsburgh  seam  reaches  a  thickness  of  n  feet. 

Much  of  the  coal  from  West  Virginia,  especially  in  the  southern  part 
of  the  state,  occurs  in  the  Pottsville  formation  and  this  formation 
seems  to  increase  in  relative  importance  in  the  states  to  the  south- 
west. The  seams  in  the  Pottsville  in  ascending  order  are  the  famous 
Pocahontas  seams,  Nos.  3,  4  and  6  of  the  Pocahontas  field.  Poca- 
hontas No.  3,  known  as  the  Thick  seam  and  lying  at  the  base  of  the 
Pottsville,  reaches  12  feet  in  thickness  though  usually  running  around 
6  feet.  Pocahontas  No.  4  also  runs  about  6  feet  in  thickness  and 
No.  6  is  not  mined  to  any  great  extent.  It  runs  up  to  5  feet  in  thick- 
ness. The  coal  of  this  field  is  semibituminous,  low  in  ash  and  sulphur 
and  therefore  suitable  for  mixing  with  high  volatile  coals  in  by-product 
ovens.  It  is  a  wonderful  steam  coal.  In  the  New  River  field  the 
lower  and  middle  Pottsville,  known  as  the  New  River  group,  carry 
the  Fire  Creek,  Beckley,  Welch,  Sewell  and  laeger  seams.  Of  these 
the  Sewell,  varying  from  2  to  5  feet,  the  Beckley  about  4  feet  and  the 
Fire  Creek,  3  to  7  feet,  are  the  most  important  and  most  largely  mined 
seams.  The  coal  is  semibituminous  and  coking.  In  the  Kanawha 
field  the  group  of  rocks  named  after  the  field  is  of  Upper  Pottsville 
age.  The  seams  are  the  Eagle,  Powellton,  Gas,  Alma,  Cedar  Grove, 
Chelton,  Winifrede,  Coalburg  and  Stockton.  Of  these  the  Eagle, 
Gas,  Cedar  Grove,  Coalburg  and  Stockton  are  important.  Some  of 
these  beds  reach  1 2  feet  in  thickness.  The  Cedar  Grove  and  Stockton 
carry  cannel  and  the  Coalburg  and  Stockton  are  known  as  the  splint 
coals.  The  coal  of  the  Kanawha  field  is  bituminous  to  semibitumi- 
nous. It  is  coking,  some  of  it  is  excellent  gas-producing  coal,  and  in 
general  it  is  of  high  grade. 

In  the  Allegheny  series  the  Lower  Kittanning,  Lower  Freeport  and 


VIRGINIA  375 

Upper  Freeport  seams  are  found.  The  first  seam  is  important  in 
three  of  the  fields  and  reaches  7  feet  in  thickness.  The  Upper  Free- 
port  is  important  in  the  northern  part  of  the  state,  in  places  reaching 
9  feet.  These  coals  are  good  steaming  and  by-product  coking  coals, 
used  chiefly  for  mixing  with  other  types.  In  the  Conemaugh  the 
Bakerstown  seam  is  worked  to  some  extent  in  the  Potomac  basin. 

In  the  Monongahela  the  Pittsburgh,  the  Redstone,  Sewickley  and 
Waynesburg  seams  all  occur  in  the  northern  fields  only,  the  Pitts- 
burgh in  the  Fairmont,  Panhandle  and  Piedmont  fields.  The  Pitts- 
burgh seam  averages  8  feet  6  inches,  of  which  7  feet  are  mined.  It 
is  a  lump  coal,  high  in  sulphur  in  places,  but  much  used  in  beehive 
coking  where  sulphur  is  low.  It  is  a  high  grade  bituminous  steam- 
ing and  domestic  fuel.  The  Sewickley  is  an  important  seam  reach- 
ing 10  feet  in  thickness.  It  is  a  good  coal,  containing  much  min- 
eral charcoal.  The  Waynesburg  is  mined  but  little. 

Virginia.1  —  Virginia  is  said  to  have  produced  the  first  bituminous 
coal  in  the  United  States,  coal  having  been  discovered  in  1700,  min- 
ing begun  in  1787  and  shipments  make  in  1789.  This  coal  occurs  in 
the  Atlantic  Coastal  region  in  rocks  of  Triassic  age  and  in  a  syn- 
clinal basin  much  cut  by  faults  and  so  intruded  by  igneous  rocks  that 
in  places-  the  coal  has  been  changed  to  natural  coke.  The  coal  is 
bituminous  to  semianthracite  and  some  of  it  is  of  high  grade.  Some 
seams  are  very  thick,  but  mining  conditions  are  bad  and  mining 
has  only  been  carried  on  intermittently.  This  field  extends  into 
North  Carolina. 

The  other  fields  of  Virginia  are  the  Pocahontas  or  Flat  Top  field,  a 
continuation  of  the  field  of  the  same  name  in  West  Virginia,  and  the 
Big  Stone  Gap  field  which  extends  into  Kentucky.  In  Frederick 
County  there  is  a  small  isolated  field,  and  another  in  Pulaski  and 
Montgomery  counties.  In  these  fields  the  coal  is  of  Mississippian  age, 
and  in  the  Pocono  formation.  This  is  geologically  the  oldest  coal  in 
the  country.  The  coal  is  semianthracite  to  anthracite  and  of  good 
quality.  It  is  mined  when  thick  enough  to  work,  and  some  seams 
reach  4  feet  or  more  in  thickness. 

1  U.  S.  Geol.  Survey,  igth  Annual  Kept.,  Pt.  II,  p.  393,  1898,  Geology  of  the  Rich- 
mo,nd  Basin,  Virginia,  by  N.  S.  Shaler  and  J.  B.  Woodworth;  also  Bull,  in,  1893,  Geology 
of  the  Big  Stone  Gap  Coal  Field  of  Virginia  and  Kentucky  by  M.  R.  Campbell;  Mineral 
Resources  of  Virginia  by  Watson,  Bulls.  9  and  12. 


376 


THE   COAL  FIELDS   OF   THE  WORLD— AMERICA 


FIG.  123.  —  Outcrop  of  the  "Big"  seam  at  Pocahontas,  Va.  with  crossbedded 
sandstone  above  it.     (Photo  by  H.  Ries.) 


FIG.  1 24.  — Breaker  for  semibituminous  coal  at  the  Merrimac  Mine,  Mef rimac,  Va. 

(Photo  by  H.  Ries.) 


KENTUCKY  377 

The  seams  mined  in  the  other  fields  are,  in  ascending  order,  the 
Darby,  Jawbone,  Kennedy,  Imboden,  Lower  Banner,  Upper  Banner 
and  Pocahontas  No.  3.  The  Pocahontas  No.  3  is  a  continuation  of 
this  seam  from  West  Virginia  and  here  it  is  of  the  same  quality  and 
averages  about  9  feet  thick.  The  other  seams  occur  chiefly  along 
the  extreme  western  part  of  the  state.  The  Upper  Banner  and  the 
Imboden  are  very  important  and  the  latter  is  a  specially  good  coking 
coal.  The  other  seams  are  all  mined  to  a  greater  or  less  extent  and 
some  of  them  run  as  high  as  10  feet  in  thickness.  They  are  Potts- 
ville  in  age  and  of  bituminous  character. 

Kentucky.1  —  The  coal  fields  of  Kentucky  occur  along  the  south- 
east and  the  northwest  borders  of  the  state,  the  southeastern  portion 
being  included  in  the  Eastern  province  and  the  northwestern  in  the 
Interior  province.  The  coal-bearing  rocks  of  the  southeastern  part 
of  the  state  are  Pottsville  and  Allegheny.  The  Pottsville  is  about 
500  feet  thick  and  carries  a  large  number  of  coal  beds.  There  are 
about  a  dozen  workable  beds,  the  main  ones  being  the  Flag,  Fire 
Clay,  Hazard,  Keokee,  Leonard,  High  Splint,  Dean,  Harlan,  Miller's 
Creek  and  Elkhorn.  These  seams  range  in  thickness  up  to  about  9 
feet.  The  Keokee  is  equivalent  to  the  Darby  seam  of  Virginia. 
The  High  Splint  as  the  name  indicates,  carries  splint  coal,  an  im- 
portant gas  coal.  The  coals  are  bituminous.  Some  seams  are  good 
coking  and  particularly  good  gas  coals.  There  is  a  good  deal  of  can- 
nel  coal  in  this  field  forming  seams,  or  bands  and  lenses  in  the  bitumi- 
nous seams. 

In  the  northwestern  section  of  the  state  the  main  seams  are  known 
as  Nos.  9,  ii  and  12,  of  which  No.  9  is  equivalent  to  No.  5  of  Illinois. 
No.  9  is  the  most  important  producer.  It  averages  about  5  feet  in 
thickness  and  lies  within  300  feet  of  the  surface.  In  places  this  seam 
is  badly  faulted.  No.  11,  lying  higher  up,  is  more  irregular  but 
thicker  in  places  than  No.  9,  being  about  6  feet  thick.  No.  12  is 
worked  in  some  areas.  The  coals  are  bituminous  and  higher  in 
volatile  matter  than  those  to  the  east.  They  are  also  high  in  sulphur 
and  ash. 

1  Annual  Kept.,  Inspector  of  Mines  of  Kentucky,  1902.  Also  Ky.  Geol.  Survey, 
series  2,  Pt.  XI,  Vol.  IV,  by  Moore;  and  Bull.  18,  1912  by  Fobs.  For  analyses  see  Ky. 
Geol.  Survey,  New  series,  Chemical  Reports. 


378  THE   COAL   FIELDS  OF  THE  WORLD— AMERICA 

Tennessee.1  —  The  Tennessee  coal  beds  occur  in  the  following 
basins:  Wartburg,  Walden,  Sewanee  and  Cumberland.  In  the 
last-named  it  is  said  the  Coal  Measures  are  over  3000  feet  thick  and 
that  they  contain  almost  100  feet  of  coal.  The  Wartburg  basin  has 
three  or  four  beds  which  are  now  worked,  one  of  which,  the  Brice- 
ville,  is  about  4  feet  thick.  In  the  eastern  part  of  the  Walden  basin 
the  beds  are  sharply  upturned,  but  for  the  most  part  the  coals  of 
Tennessee  lie  quite  flat.  The  best  known  seams  in  the  state  are  the 
Sewanee,  Jellico  and  Coal  Creek.  The  coals  are  all  bituminous  and 
most  of  them  are  suitable  for  steam,  domestic  purposes  and  gas  manu- 
facture. The  Coal  Creek  coal  is  used  in  coking. 

Georgia.2  —  Only  167  square  miles  are  underlain  with  coal  in  this 
state  and  the  coal  is  all  of  Pottsville  age.  The  Walden  basin  of 
Tennessee  crosses  through  Georgia  into  the  Warrior  and  Blount 
Mountain  basins  of  Alabama.  The  Lookout  basin  extends  into 
Walker  County,  Georgia.  In  this  basin  the  coal  is  of  high  quality, 
being  semibituminous  to  semianthracite  and  low  in  sulphur.  Part 
of  it  is  coked.  The  rest  of  the  coal  in  the  state  is  bituminous. 


4000 


FIG.  125.  —  Structure  section  in  the  northern  part  of  the  Cahaba  Coal  Field,  Ala. 
(By  Charles  Butts,  U.  S.  Geol.  Survey.) 

Alabama.3  —  The  Coal  Measures  in  crossing  from  Georgia  widen 
out  in  Alabama  and  form  four  important  basins,  the  Coosa,  Ca- 
haba, Warrior  and  Plateau  basins.  The  Coosa  basin  is  a  deep  syn- 

1  Hayes,  C.  W.,  The  Southern  Appalachian  Coal  Field.    U.  S.  Geol.  Survey,  22nd 
Annual  Rept.  Pt.  Ill,  p.  227,  1902.    Also  Resources  of  Tennessee  I,  No.  5,  by  Ashley. 

2  McCallie,  Georgia  Geol.  Survey,  1904. 

3  Butts,  C.,  The  northern  part  of  the  Cahaba  Coal  Field,  Ala.    U.  S.  Geol.  Survey, 
Bull.  316,  p.  76,  1907.     Also  reports  by  McCalley  on  the  Warrior  Field,  1900  and  by 
Gibson  on  the  Coosa  Field,  Ala.  Geol.  Survey,  1895. 


MICHIGAN 


379 


cline  of  unexplored  depth  about  60  miles  long  by  6  wide.  It  con- 
tains a  large  number  of  seams.  Two  seams  are  worked,  the  Eureka 
and  the  Coal  City.  This  basin  is  considerably  faulted  and  folded. 

The  Cahaba  basin  covers  about  350  square  miles  and  is  very  deep, 
the  coal  beds  probably  extending  more  than  3000  feet  below  the  sur- 
face, (Fig.  125).  The  thickness  of  the  Coal  Measures  is  usually 
considered  about  5500  feet.  There  are  about  ten  seams  mined  and 
the  coal  is  bituminous  and  coking. 

The  Warrior  is  the  most  important  of  the  basins.  The  best  known 
seams  are  the  Pratt  and  the  Mary  Lee  as  they  furnish  most  of  the 
coal  mined  in  the  Birmingham  district,  and  this  coal  furnishes  the 
coke  after  washing.  The  Pratt  seam  in  places  reaches  16  feet  in 
thickness.  Besides  these  two  seams  16  other  beds  are  worked  in 
this  basin.  The  Plateau  field  is  small  and  undeveloped  but  it  con- 
tains many  good  beds.  The  coals  in  Alabama  are  all  of  Pottsville 

age  and  bituminous  in  character. 

\_ 

T/tc  Interior  Province 

Michigan.1  —  The  coal  basin  of  Michigan  contains  a  compara- 
tively flat-lying,  slightly  faulted  series  which  includes  the  Potts- 
ville and  Allegheny  formations  of  the  Pennsylvanian  and  which  is 


FIG.  126.  —  Structure  section  in  Bay  County,  Mich.,  from  the  Amelith  Mine  to  the 
Central  and  Michigan  mines.  It  shows  glacial  drift  overlying  the  eroded  surface  of 
the  Coal  Measures.  (After  Lane,  U.  S.  Geol.  Survey.) 

overlain  by  glacial  drift.  There  are  seven  coal-bearing  horizons  of 
significance  and  these  are  known  as  the  Lower  Coal,  Lower  Rider, 
Saginaw,  Middle  Rider,  Lower  Verne,  Upper  Verne  and  Upper  Rider. 
The  seams  are  very  irregular  in  thickness  and  character  and  they 
change  rapidly  from  place  to  place  (Fig.  126).  The  coal  is  of  bitu- 

1  Lane,  A.  C.,  The  Northern  Interior  Coal  Field.    U.  S.  Geol.  Survey,  22nd  Annual 
Report.    Pt.  Ill,  p.  313,  1902.    Also  Geol.  Survey,  Michigan,  Vol.  VIII,  Pt.  2. 


300 


100 


Rallsford  Shale 
Red 


Shaly  Limestone 


^\  Conglomerate 


(380) 


Sandy  Shale 
Conglomerate 


Fie.  127.  —  Columnar  sections  of  the  Coal  Measures  in  Illinois. 
(Illinois  Geol.  Survey.) 


ILLINOIS  381 

minous  rank,  is  non-coking  and  dry  and  is  used  for  steam,  producer 
gas,  domestic,  and  related  purposes. 

Illinois.1  —  Illinois  has  the  largest  area  of  Carboniferous  coals  of 
any  of  the  states  as  nearly  three-fourths  of  the  state  is  underlain  by 
Coal  Measures.  The  basin  is  comparatively  flat  with  from  1500 
to  2000  feet  of  measures  near  the  center.  The  seams  are  faulted  in 
many  places  by  small  faults  and  near  the  Kentucky  border  the  beds 
are  caught  in  overturned  folds  and  considerably  faulted.  The  fields 
are  covered  with  glacial  drift  so  that  prospecting  is  often  carried  on 
with  difficulty,  shafts  being  necessary  to  reach  the  coal.  The  shafts 
in  the  state  run  from  25  feet  to  1000  feet  in  depth  but  the  majority 
are  probably  less  than  300  feet.  The  beds  as  a  rule  are  extensive 
and  persistent.  The  coals  are  both  coking  and  dry  but  the  coals 
which  will  coke  are  high  in  sulphur,  the  average  running  around  3 
per  cent  for  many  of  the  mines,  and  they  are  therefore  unsuitable  for 
commercial  coke.  They  are  used  mostly  for  domestic,  steam  and 
locomotive  purposes.  Much  of  the  coal  is  washed  and  sized.  The 
longwall  method  of  mining  is  used  to  a  considerable  extent  in  this 
state. 

In  geological  age  the  coals  are  Allegheny  and  Pottsville.  The 
most  important  seams  are  Nos.  2,  5,  6,  and  7.  No.  i  seam  and  a 
few  others  occur  in  the  Pottsville  and  are  worked  in  the  southern 
part  of  the  state,  No.  i  probably  corresponding  to  the  Mercer 
horizon  farther  east.  No.  2  occurs  in  the  Carbondale  formation, 
which  is  regarded  as  equivalent  to  the  Allegheny,  and  is  a  very  per- 
sistent bed  averaging  around  4  feet  in  thickness.  It  is  regarded  by 
some  as  equivalent  to  the  Clarion  coal  of  Ohio  and  Pennsylvania. 
In  places  it  contains  many  sulphur  balls.  These  concretions  are 
also  common  in  No.  5  and  in  the  roof  shale  above  that  seam.  No.  5 
runs  about  4  to  5  feet  in  thickness  and  is  an  important  seam.  No.  6, 
or  the  "Belleville"  seam,  is  probably  the  most  persistent  in  the 
state,  and  in  the  western  part  is  mined  to  a  depth  of  about  800  feet. 
It  runs  from  5  to  6  feet  in  thickness  over  large  areas  and  in  places  it 
reaches  9  feet.  No.  7  is  mined  around  Danville  and  is  from  5  to 
7  feet  in  thickness.  It  contains  much  sulphur  which  can  be  read- 

1  Ashley,  G.  H.,  The  Eastern  Interior  Coal  Field,  U.  S.  Geol.  Survey,  22nd  Annual 
Report,  Pt.  Ill,  p.  271;  Bulls,  i  to  15,  111.  Coal  Mining  Investigations,  at  University 
of  Illinois,  also  Bulls.  4,  8  and  16,  Illinois  Geol.  Survey. 


382  THE   COAL  FIELDS   OF  THE  WORLD— AMERICA 

ily  separated  by  picking  and  washing.  Another  higher  seam,  No.  8, 
is  mined  in  some  localities. 

Indiana.1  —  The  coal  beds  of  Indiana  occur  along  the  western 
border  of  the  state  and  the  coal  is  all  of  bituminous  rank.  It  occurs 
in  the  Pottsville  and  Allegheny  formations  as  in  Illinois.  Work- 
able coal  is  found  at  eight  horizons  at  least  and  six  of  these  are 
producing.  The  main  seams  are  known  as  the  Lower  and  Upper 
Block,  the  Minshall,  and  seams  Nos.  2,  3,  4,  5,  6,  and  7.  No.  8  is 
thin.  The  lower  coals,  including  the  Block  and  Minshall  seams, 
are  of  Pottsville  age  and  are  characterized  by  being  non-coking, 
pure  and  dry  coals  which  break  into  rectangular  blocks.  The  seams 
usually  run  about  3  feet  in  thickness  as  an  average.  The  other 
seams  are  classed  as  bituminous  coals  of  Allegheny  age  and  they 
run  from  3  to  10  feet  in  thickness  with  5  feet  a  very  common  figure 
and  the  beds  very  persistent.  The  shafts  run  from  50  to  450  feet 
in  depth  for  most  of  the  field. 

Iowa.2  —  The  coal  fields  lie  in  the  southern  and  central  part  of  the 
state  and  cover  about  12,500  square  miles.  The  beds  are  of  lower 
Pennsylvanian  age,  as  in  Illinois  and  Indiana,  and  they  occur  in  the 
Pottsville  and  Allegheny  formations.  These  are  represented  by 


s.w. 


FIG.  128." — Ideal  cross-section  of  the  formations  in  Mahaska  County,  Iowa,  illus- 
trating the  character  of  the  Coal  Measures  in  Iowa.  (After  H.  Hinds,  Iowa  Geol. 
Survey.) 

two  series  of  rocks,  the  lower,  or  Des  Moines,  and  the  upper,  or 
Missouri  group.  The  Missouri  group  contains  much  limestone  and 
little  coal,  the  Nodaway  bed  being  the  only  one  mined,  and  it  fur- 
nishes less  than  i  per  cent  of  the  coal  mined  in  the  state.  It  is  16  to 
20  inches  thick  and  fairly  persistent.  The  Des  Moines  group,  al- 
though consisting  chiefly  of  shale  and  sandstone,  has  a  thin  lime- 
stone bed  near  the  middle.  It  carries  a  well-known  seam,  the  Mystic 
or  Centreville  bed,  which  is  persistent  and  extends  over  into  Mis- 

1  Ashley,  G.  H.,  Stratigraphy  and  coal  beds  of  Indiana  Coal  Field.    U.  S.  Geol.  Survey, 
Bull.  381,  p.  9,  1908;  also  Indiana  Dept.  of  Geol.  and  Nat.  Res.,  33d  Annual  Rept.  1909. 

2  Hinds,  Henry,  The  coal  deposits  of  Iowa.    Iowa  Geol.  Survey,  Vol.  XIX,  1908. 


MISSOURI  383 

souri.  The  lower  part  of  the  Des  Moines  group  carries  a  number  of 
beds  and  while  they  locally  run  up  to  10  feet  or  more  the  average 
is  about  5  feet  in  thickness.  The  seams  are  characterized  by  their 
lack  of  persistency  and  their  sudden  changes  in  quality.  They  lie 
nearly  flat  and  while  faults  are  numerous  they  are  not  large.  The 
coal  is  dry,  non-coking,  comparatively  high  in  sulphur  and  used  al- 
most entirely  for  domestic  and  railroad  purposes.  The  coal  field 
is  covered  with  glacial  drift  so  that  there  are  few  outcrops  and  pros- 
pecting is  difficult.  For  this  reason  little  is  known  about  many  of 
the  seams.  Much  of  the  coal  lies  400  to  500  feet  below  the  surface. 

Missouri.1  —  The  same  geological  series  occur  in  Missouri  as  in 
Iowa,  the  Pennsylvanian  rocks  being  divided  into  the  upper,  or  Mis- 
souri group  and  a  lower,  or  Des  Moines  group.  The  upper  is  quite 
largely  a  limestone  series  and  carries  little  coal.  Most  of  the  seams 
occur  in  the  Des  Moines  group.  Those  near  the  base  are  very  ir- 
regular and  lack  persistency  while  the  seams  associated  with  the 
thin  limestone  beds  higher  up  in  the  group  are  very  persistent  and 
comparatively  regular.  The  main  fields  are  the  Bevier  where  the 
Bevier  seam  is  3  to  6  feet  thick;  the  Lexington  with  a  seam  14  inches 
to  2  feet  thick  which  is  mined  by  the  longwall  method;  the  South- 
western field;  the  Novinger  field  with  a  seam  3^  feet  thick  and  prob- 
ably equivalent  to  the  Bevier  seam;  the  Marceline  where  a  29-inch 
seam  is  mined;  and  the  Mendota  where  the  coal  lies  at  about  the  same 
horizon  as  that  in  the  Lexington  and  the  bed  is  supposed  to  be  equiva- 
lent to  the  Centreville  seam  of  Iowa.  It  is  not  mined  to  any  great 
extent.  There  are  a  number  of  "  pockets  "  of  coal  lying  in  isolated 
areas  east  of  the  main  field.  Some  of  these  are  very  thick  but  limited 
in  extent,  Parker  mentioning  one  where  the  coal  is  80  feet  thick 
and  consists  of  ordinary  bituminous  coal  and  cannel. 

The  seams  of  Missouri  mostly  lie  nearly  flat  and  the  faults,  while 
numerous,  are  small.  There  are  many  horsebacks,  concretions  and 
other  obstructions  in  mining.  Owing  to  the  shallowness  of  the  seams 
in  parts  of  the  state,  approximately  20  per  cent  of  the  annual  output 
is  produced  by  the  use  of  steam  shovels.  The  coals  are  not  high  grade 
as  they  are  high  in  sulphur,  moisture  and  ash.  They  are  used  as 
domestic  and  steaming  fuels. 

1  Hinds,  H.,  Missouri  Bur.  Mines  and  Geol.,  Vol.  XI,  2nd  series,  1912. 


384  THE  COAL  FIELDS  OF  THE  WORLD— AMERICA 

Kansas.1  —  About  20,000  square 
miles  are  underlain  by  Pennsyl- 
vanian  rocks  in  this  state  and  it 
is  estimated  that  nearly  three- 
fourths  of  the  area  will  prove  pro- 
ductive. The  field  lies  in  the 
eastern  portion  of  the  state  and 
the  most  important  and  best- 
known  localities  are  in  Cherokee 
and  Crawford  counties  which  fur- 
nish over  90  per  cent  of  the  coal. 
The  geological  series  are  much 
like  those  of  Iowa  only  less  dis- 
tinctly marked,  with  limestone 
more  abundant  in  the  lower  series 
and  the  coal  distributed  more 
widely  through  the  various  forma- 
tions. The  thickness  of  the  meas- 
ures is  about  3000  feet  and  on 
the  whole  the  beds  lie  nearly  flat, 
(Fig.  129).  The  Cherokee  seam  is 
the  main  bed  and  it  varies  from  3 
to  10  feet  in  thickness  with  an 
average  of  about  40  inches.  This 
coal  is  washed  and  it  may  then 
be  coked  but  most  of  it  is  used  for 
locomotive  and  domestic  fuel. 
Much  coal  is  mined  by  stripping 
methods  where  it  lies  near  the 
surface.  The  weathered  coal  from 
the  pits  is  non-coking  because  of 
oxidation.  It  is  used  raw  in  some 
of  the  zinc  furnaces. 

In   the  Leavenworth  district  a 

1  Howarth  and  Crane,  Kansas  Geol. 
Survey,  Vol.  Ill,  1898.  Also  the  Western 
Interior  Coal  Field  by  H.  F.  Bain,  U.  S. 
Geol.  Survey,  22nd  Annual  Report,  p.  339, 
1902. 


ARKANSAS 


385 


thin  seam  is  mined  at  a  depth  of  700  to  1150  feet.  This  is  the  only 
deep  mining,  according  to  Parker,  which  is  carried  on  in  the  Western 
Interior  field.  Another  area  occurs  in  the  Osage  County  district  where 
a  seam  is  mined  at  a  horizon  about  2000  feet  above  the  Cherokee 
bed. 

A  small  lignite  field  also  occurs  in  Kansas  with  coal  of  Cretaceous 
age  which  is  mined  for  local  consumption. 

Oklahoma.1  —  The  rocks    carrying   coal   in  .  NMIESOF 
Oklahoma  apparently  represent  most  of  the    COAL  BEOS 
Pennsylvanian  formations.  There  are  two  main 
fields,  the  Cherokee  and  the  Choctaw,  the  latter 
much  the  more  important.    The  coals  vary  from 
ordinary  bituminous  to  semibituminous.    Some 
of  the  coals  are  coking  and  a  number  of  ovens  Paris — 
are  operated,  but  most  of  the  coke  is  too  high  in 
sulphur  for  iron  furnaces.    There  are  about  ten  Charleston, 
workable  seams  of  which  the  following  are  the 
best  known:    Hartshorne,  Dawson,  Henryetta, 
McAlester,  Cavanal  and  Witteville,  upper  and 
lower.     The  Henryetta  is  the  most  important 
seam  in  the  Cherokee  field  and  averages  about 
3  feet  in  thickness.     The  Hartshorne   seams  H" 
run  from  2  to  7  feet   in    thickness   and    the 
McAlester  coals  about  4  feet.     The  strata  are 
much  folded  and  faulted  in  parts  of  the  fields, 
and  many  of  the  mines  carry  considerable  gas. 





uPPer 

Hartshorne 


Fort  Smith 
375-425 


Spadra 
400-500 


EG.  130  .  —  Generalized 
columnar  section  of  the 
coal-bearing  rocks  of  Ar- 
kansas. (After  Collier, 
U.  S.  Geol.  Survey.) 


Gulf  Province 

Arkansas.2  —  The  coal  beds  are  well  exposed 
in  this  field  and  they  have  suffered  consider- 
able folding,  faulting  and  erosion.  They  are 
of  Pennsylvanian  age,  Pottsville  to  Allegheny, 
and  the  coals  vary,  even  in  the  same  seam, 
from  bituminous  to  semibituminous  and  semianthracite,  the  fuel 
ratio  increasing  from  about  5  on  the  western  side  of  the  field  to 

1  Taff,  J.  A.,  The  Southwestern  Coal  Field.     U.  S.  Geol.  Survey,  22nd  Annual  Rept., 
Pt.  Ill,  p.  367,  1902. 

2  Collier,  A.  J.,  The  Arkansas  Coal  Field.    U.  S.  Geol.  Survey,  Bull.  316,  p.  137,  1906. 


386  THE   COAL  FIELDS  OF  THE  WORLD— AMERICA 

nearly  8  on  the  east.  There  are  three  seams,  of  which  the  Harts- 
horne,  corresponding  to  the  seam  of  the  same  name  in  Oklahoma,  is 
the  most  important.  This  seam  is  about  8  feet  thick  and  it 
supplies  nearly  all  the  coal  of  the  state.  Other  seams  which  are 
mined  a  little  are  the  Charleston,  lying  about  700  feet  above  the 
Hartshorne  and  the  Paris  about  1000  feet  above  the  latter  seam. 
There  is  some  lignite  lying  in  the  lowlands  southeast  of  Little  Rock. 
It  is  mined  to  a  small  extent  but  is  practically  undeveloped.  It  is 
of  Tertiary  age  and  listed  under  the  Gulf  province. 

Texas.1  —  There  are  three  fields  in  Texas  with  coals  of  three  differ- 
ent ages  and  grades.  One  of  the  fields  in  the  north-central  part  of 
the  state  belongs  to  the  southwestern  field  of  the  Interior  province. 
The  coal  is  Pennsylvanian  in  age  and  mostly  of  bituminous  rank  al- 
though there  are  portions  of  it  which  might  be  more  properly  classed 
as  subbituminous.  The  Pennsylvanian  is  here  divided  into  the  fol- 
lowing divisions  in  ascending  order:  Millsap,  Strawn,  Canon,  Cisco 
and  Albany.  The  structure  is  simple,  the  basin  dipping  gently  north- 
westward and  westward.  There  are  three  workable  seams,  two  of 
which  are  worked.  They  are  thin,  in  few  places  more  than  2  feet. 
No.  i  seam  is  in  the  Millsap  and  the  Cisco  formation  carries  two 
workable  beds,  one  known  as  No.  7  which  is  the  highest  bed  worked. 
The  coals  are  high  in  sulphur  and  ash  and  are  therefore  used  mostly 
for  railroad  and  other  steaming  purposes. 

The  Eagle  Pass  field  is  a  small  one  on  the  Rio  Grande  and  it  ex- 
tends over  into  Mexico.  The  strata  are  considered  to  be  of  Upper 
Cretaceous  age  and  the  coal  is  subbituminous  in  rank.  The  beds  run 
from  5  to  6  feet  in  thickness  and  dip  steeply  in  parts  of  this  field. 

The  large  lignite  field  extends  across  the  state  from  the  Sabine 
River  to  the  Rio  Grande.  The  rocks  are  of  Eocene  age  and  the  coal 
varies  from  woody  lignite  to  subbituminous  grade.  The  latter  oc- 
curs in  the  Laredo  field  along  the  Rio  Grande  where  the  rocks  have 
been  compressed  by  the  uplift  of  the  Sierra  Madre  Oriental,  a  little 
to  the  southwest,  in  Mexico.  Campbell  has  pointed  out  that  in  the 
southern  part  of  the  state  the  lignite  consists  chiefly  of  trees  and 
other  coarse  fragments  of  plants  while  in  the  northern  part  there  is  a 
much  greater  proportion  of  spores,  seeds  and  other  related  vegetal 

1  Dumble,  E.  J.,  Texas  Geol.  Survey,  1892.  Phillips,  W.  B.,  and  Worrell,  S.  H., 
The  fuels  used  in  Texas.  Bull.  University  of  Texas  No.  307, 1913.  (Numerous  analyses.) 


NEW  MEXICO  387 

matter  in  the  coal.  The  lignite  occurs  in  the  three  upper  divisions  of 
the  Eocene  at  comparatively  shallow  depths  and  the  beds  vary  from 
a  few  inches  to  about  25  feet  in  thickness.  Those  being  mined  usually 
run  between  4  and  8  feet,  except  in  Webb  County  where  the  coal 
is  subbituminous  and  the  seams  mined  are  less  than  3  feet  thick.  The 
lignite  field  belongs  in  the  Gulf  province.  The  known  field  is  much  less 
than  the  probable  field  as  the  seams  are  largely  unprospected.  The 
lignite  is  largely  used  for  domestic  purposes,  for  steam,  and  in  gas 
producers. 

The  Northern  Great  Plains  and  Rocky  Mountain  Provinces 
These   two  provinces   are  considered  together  here  since  many 
states  are  included  in  both  of  them. 

Arizona.  —  Arizona  is  not  yet  a  producer  and  has  not  been  well 
prospected,  but  it  contains  several  fields  and  a  large  reserve  of  coal 
of  subbituminous  quality.  It  is  of  Cretaceous  age.  The  main  area 
is  the  Black  Mesa  field,  a  flat,  open,  synclinal  basin  with  coal  in  thin 
benches.  The  other  field  of  which  something  is  known  is  the  Deer 
Creek  field  in  the  copper-bearing  region  of  the  state.  This  forms  a 
simple  synclinal  basin  with  the  rocks  greatly  broken  and  the  coal  of 
little  value  in  the  southwestern  part.  Two  beds  of  workable  thick- 
ness running  from  24  to  30  inches  are  reported  by  Campbell. 

New  Mexico.1  —  This  state  contains  coal  varying  in  rank  from 
subbituminous  to  anthracite,  the  latter  occurring  where  the  coal  has 
been  locally  metamorphosed  by  igneous  intrusions  as  in  the  Cerillos 
field.  There  are  five  fields:  (a)  The  Raton  field  of  Coif  ax  County, 
which  is  an  extension  of  the  Trinidad  field  of  Colorado  and  will  be 
discussed  under  that  state;  (b)  The  San  Juan  River  region,  in- 
cluding the  Gallup  and  Monero  producing  districts,  and  extending 
into  Colorado;  (c)  A  little-known  area  in  Valencia,  Bernalillo  and 
Sandoval  counties;  (d)  The  Los  Cerillos  field  in  Santa  Fe  County; 
and  (e)  The  Whiteoaks  field  in  Lincoln  County.  Outside  of  the 
Raton  field  the  coal  is  practically  all  subbituminous  and  all  the 
coals  of  the  state  are  regarded  as  of  Upper  Cretaceous  age,  chiefly 
Montana,  except  in  a  very  limited  area  near  Pecos,  carrying  lower 
Pennsylvanian  coal.2  Near  Monero  the  coal  is  bituminous.  Some 

1  Storrs,  L.  S.,  The  Rocky  Mountain  Coal  Field.     U.  S.  Geol.  Survey,  22nd  Annual 
Rept.  Pt.  Ill,  p.  449.     Also  U.  S.  Geol.  Survey,  Bulls.  285,  316,  381,  471  and  531. 

2  Gardner,  J.  H.,  U.  S.  Geol.  Survey,  Bull.  381,  p.  449,  1908. 


388 


THE   COAL   FIELDS  OF  THE  WORLD— AMERICA 


of  the  fields,  as  for  example  the  Carthage  field,  are  complexly  faulted 
and  igneous  intrusions  are  common. 

Colorado.1  —  This  state  is  the  largest  coal  producer  west  of  the 
Mississippi.  The  fields  of  the  state  are  as  a  rule  divided  into  the 
Eastern,  the  Park  and  the  Western  groups.  The  Eastern  group  con- 
tains the  following  fields:  Trinidad,  Canon  City  and  South  Platte. 
The  Park  contains  the  South,  Middle  and  North  Park.  The  Western 
group  is  the  largest  and  includes  the  Yampa  field  in  the  north,  the 
Danforth  Hills,  White  River  and  Grand  Hogback  to  the  north  of 
Grand  River,  the  Glenwood  Springs  basin,  Crested  Butte  and  Grand 
Mesa  just  south  of  the  Grand  River,  Book  Cliffs  near  Grand  Junc- 
tion and  the  Durango  field  in  the  southwestern  part  of  the  state. 


1000 


2000 


3000  Feet 


FIG.  131.  —  Section  between  Occidental  and  Oakdale  mines,  northwest  of  La  Veta.  Colo. 
(After  G.  B.  Richardson,  U.  S.  Geol.  Survey.) 

The  coals  are  subbituminous  in  the  North  Park  field  and  Denver  re- 
gion, partly  bituminous  and  partly  subbituminous  in  the  Durango 
field,  partly  bituminous  and  partly  anthracite  in  the  Uinta  Basin 
region,  and  partly  subbituminous,  partly  bituminous,  and  partly 
anthracite  in  the  Yampa  field.  The  other  fields  all  contain  bitumi- 
nous coals  of  varying  grades.  The  anthracite  and  other  high-carbon 
coals  occur  in  those  areas  where  the  coal  has  been  highly  compressed 
or  heated  by  igneous  rocks  and  thus  devolatilized.  The  same  seam 
may  carry  coal  ranging  from  bituminous  to  anthracite,  the  latter 
near  the  igneous  rocks. 

The  age  of  the  Colorado  coals  is  mostly  Upper  Cretaceous,  the 
bulk  of  the  coal  occurring  in  the  Mesaverde  formation  of  the  Mon- 

1  U.  S.  Geol.  Survey,  22nd  Annual  Rept.,  Pt.  Ill,  p.  427.  Also  Bulls.  297  (Yampa) 
316  (Danforth  Hills,  Book  Cliffs  and  Durango)  317  (Book  Cliffs)  381  (Denver  Basin, 
South  Park,  Colorado  Springs,  Trinidad)  Folio  No.  9  (Crested  Butte). 


COLORADO 


389 


tana  series.     Some  is  Laramie,  a  little  Dakota  and  a  small  amount 
of  Eocene  age. 

The  Trinidad  field  forms  part  of  the  Raton  Mountain  area  which 
extends  over  into  New  Mexico.  It  is  divided  into  the  Trinidad 
district  to  the  south  and  Walsenburg  district  to  the  northeast.  The 
rocks  are  of  Laramie  age  and  the  coal-bearing  series  varies  in  thick- 
ness from  1500  to  3000  feet.  In  this  field  there  are  as  many  as  eight 


,_-,^'x'vx'</;~\  v  A  "*•  r\.  s  ^  —  Vs"  /  /  \*  *""•  v    -N  X  -"  \    >  ^  ^  '  s  •—  ./      i  yS-N    ^^/  x"^  /  \  /^x  ^  v  ""-t  ^ . N|  _    f* .   • 


-SCALE  IN  FEET 


FIG.  132.  —  Sills  of  igneous  rock  in  "Laramie"  formation  and  bed  of  natural  coke, 
in  Purgatory  Valley,  near  Trinidad,  Colo.  (After  G.  B.  Richardson,  U.  S.  Geol. 
Survey.) 

workable  beds,  varying  from  2  to  14  feet  in  thickness  in  the  lower  coal- 
bearing  group  of  beds,  which  is  about  250  feet  thick.  These  beds 
lie  just  above  the  Trinidad  sandstone,  and  about  500  feet  above  the 
sandstone  is  the  middle  coal-bearing  group  carrying  at  least  four 
seams,  2  to  4  feet  thick.  Lying  about  1000  feet,  on  the  average, 
above  the  Trinidad  sandstone,  is  the  upper  coal-bearing  group  of 
shales  carrying  several  seams,  but  these  are  unimportant  so  far  as 
known. 


3QO  THE   COAL  FIELDS  OF  THE  WORLD— AMERICA 

The  coal  from  the  Trinidad  field  is  bituminous,  that  from  the 
northern  part  being  non-coking  while  that  from  the  southern  makes 
an  excellent  coke.  An  interesting  occurrence  in  the  Walsenburg  dis- 
trict is  the  niggerhead  coal  described  on  page  235.  The  coal  in  some 
of  the  seams  adjacent  to  igneous  rocks  forms  peculiar  spherical  struc- 
tures known  locally  as  "  niggerheads  "  and  consisting  of  quite  high- 
grade  coal.  Such  bodies  have  been  found  in  a  few  cases  in  other 
fields  where  igneous  rocks  have  intruded  the  coal  seams.  In  some 
places  considerable  natural  coke,  or  carbonite,  has  been  formed  by 
igneous  rocks  in  the  Trinidad  field.  The  structure  of  this  region 
varies  from  places  where  the  beds  are  practically  flat  and  undis- 
turbed to  others  where  they  are  highly  folded,  faulted  and  intruded 
with  igneous  rocks. 

The  Canon  City  field  is  a  small  one  containing  bituminous  coal 
in  the  Laramie  formation.  The  rocks  vary  from  flat-lying  to 
steeply  dipping. 

The  South  Platte  field  includes  the  counties  around  Denver  and 
contains  subbituminous  coal  of  Laramie  age.  The  beds  are  com- 
paratively flat  except  where  the  strata  are  more  closely  folded  near 
the  mountains  along  the  western  border.  The  beds  are  fairly  thick 
in  parts  of  the  field  and  there  are  four  of  them  in  most  places.  The 
coal  is  not  of  high  grade  and  it  is  used  chiefly  for  domestic  and  steam 
purposes. 

The  North  Park  field  is  reported  to  carry  very  thick  coals  of  bitu- 
minous rank,  some  seams  as  high  as  30  feet  in  thickness,  but  little 
mining  is  done.  No  mining  is  now  carried  on  in  the  South  Park 
field  although  some  mines  were  operated  during  the  last  century. 

The  Yampa  field  occupies  a  large  synclinal  basin  with  several 
minor  anticlines  and  synclines  running  nearly  parallel  across  it.  The 
strata  are  in  a  few  places  greatly  disturbed  by  faults,  but  as  a  rule 
the  faults  are  of  little  importance.  Most  of  the  basin  is  not  badly 
folded.  The  coal-bearing  series  is  the  Mesaverde  of  the  Montana 
series  of  Upper  Cretaceous.  This  series  is  about  3500  feet  thick 
and  it  is  overlain  by  approximately  2000  feet  of  Lewis  and  Laramie 
strata,  the  Laramie  carrying  thin  beds  of  coal.  The  thickness  of 
the  seams  varies  up  to  about  12  feet.  In  the  Anthracite  Range, 
especially  around  Pilot  Knob,  there  is  some  anthracite  and  natu- 
ral coke  produced  by  action  of  the  igneous  rocks  which  sometimes  affect 


UTAH  391 

the  coal  for  a  distance  of  50  feet  or  more.  The  coals  in  this  field 
vary  from  subbituminous  to  anthracite. 

In  the  Danforth  Hills  and  Grand  Hogback  fields,  which  represent 
part  of  the  Uinta  basin  region,  there  is  one  coal-bearing  horizon, 
the  Mesaverde,  and  this  is  a  distinct  ledge-making  formation  be- 
cause of  the  sandstone  which  it  contains.  The  structure  of  this 
region  is  simple  as  there  are  broad  basins  with  minor  folds,  and 
faults  are  not  numerous.  There  are  as  many  as  seven  seams  varying 
in  thickness  from  4  to  48  feet,  making  an  aggregate  thickness  of 
coal  of  about  108  feet.  Some  of  these  seams  are  separated  by  over 
1000  feet  of  intervening  strata.  The  mines  through  this  region  are 
subject  to  much  trouble  with  explosive  gas  and  spontaneous  com- 
bustion of  the  coal. 

In  the  Crested  Butte  district  of  the  Uinta  Basin  region  consider- 
able anthracite  has  been  formed  by  igneous  activity  and  both  bitu- 
minous coal  and  anthracite  occur  in  this  field. 

The  Durango  field,  lying  in  the  southern  part  of  the  state,  extends 
over  into  New  Mexico  in  the  San  Juan  River  region  and  of  the  73,900 
square  miles  in  this  field  only  1900  lie  in  Colorado.  The  coals  in 
this  field  vary  from  subbituminous  to  bituminous.  Their  geological 
age  is  Upper  Cretaceous,  Dakota,  Montana  and  Laramie.  The 
Mesaverde  formation  of  the  Montana  carries  the  best  coals,  the 
seams  averaging  around  5  or  6  feet  in  thickness.  The  Dakota  coals 
are  not  of  much  inportance,  and  while  the  seams  in  the  Laramie  are 
very  thick  —  one  reported  to  be  as  much  as  80  feet  —  the  coal  is 
of  an  inferior  quality  to  that  from  the  Mesaverde  formation.  The 
coal  from  several  localities  in  the  latter  formation  makes  good  coke. 
The  structure  of  the  basin  is  comparatively  simple  except  around 
Gallup  and  in  the  southern  end  of  the  basin  where  the  rocks  have 
been  highly  disturbed. 

Utah.1  —  The  Uinta  Basin  region  contains  the  largest  area  of  coal 
lands  in  the  state  and  it  extends  across  the  Colorado  boundary  from 
the  Crested  Butte  district.  The  beds  are  deeply  covered,  going  well 
below  3000  feet  in  the  centre  of  this  basin,  and  probably  out  of  reach 
of  mining  operations.  The  coals  are  bituminous  and  coking.  Prac- 
tically all  the  coal  mined  in  the  state  comes  from  the  vicinity  of 

1  U.  S.  Geol.  Survey,  22nd  Annual  Rept.,  Pt.  Ill,  p.  453.  Also,  Bulls.  316,  341,  415 
and  47 1. 


392 


THE   COM.   FIELDS   OF   THE   WORLD— AMERICA 


I 


II 


l« 


§•§ 

15 

I! 


Sunnyside,  Castlegate,  Winterquarters  and  Clear 
Creek.  There  are  about  20  seams  in  this  dis- 
trict, with  a  maximum  individual  thickness  of 
about  20  feet.  The  seams  occur  in  the  base  of 
the  Mesaverde  (Montana)  of  the  Upper  Creta- 
ceous. In  the  Coalville  field,  which  is  a  small 
one,  two  seams  running  about  7  to  14  feet  in 
thickness  are  mined.  The  coal  is  in  the  Colorado 
series. 

The  other  field  is  the  Colob  Plateau  field  which 
carries  a  seam  in  the  Colorado  series  from  i  to 
10  feet  thick.  The  coal  varies  from  bituminous 
to  semianthracite  and  impure  anthracite.  Be- 
cause of  the  closely  folded  nature  of  some  of 
the  strata  much  of  the  coal  is  of  poor  quality. 
In  Kane  County  cannel  occurs,  and  a  little  an- 
thracite is  found  in  Iron  County. 

Wyoming.1  —  Wyoming  probably  contains  the 
second  largest  resources  in  coal  of  any  state  in 
the  Union,  North  Dakota  coming  first.  The 
coals  of  Wyoming  are,  however,  of  higher  grade 
than  those  in  North  Dakota  since  the  coal  in  the 
latter  state  is  all  lignite  and  that  in  the  former 
is  not  below  subbituminous,  while  a  considerable 
amount  of  it  is  bituminous  in  rank. 

The  following  regions  are  recognized:  Black 
Hills  and  Powder  River  regions  of  the  Great 
Plains  province;  the  Bighorn  Basin,  Wind  River 
Basin,  Green  River  Basin,  Hams  Fork  region, 
and  the  Hanna  field,  all  of  the  Rocky  Mountain 
province.  Of  these  areas  the  Powder  River 
region  is  the  largest.  It  lies  between  the  Bighorn 
Mountains  and  Black  Hills  and  runs  from  the 
Platte  River  to  the  Montana  boundary.  It 
represents  the  extension  of  the  Fort  Union 
region  of  North  Dakota.  About  11,000  square 

1  U.  S.  Geol.  Survey,  22nd  Annual  Rept.,  Pt.  Ill,  p.  439. 
Also,  Bulls.  225,  260,  285,  316,  341,  381,  47i  and  531,  and 
Prof.  Paper  56. 


NORTH  AND  SOUTH  DAKOTA  393 

miles  are  underlain  with  coal  beds  more  than  3  feet  thick.  The  rocks  of 
the  field  are  of  Fort  Union  (Eocene)  age  and  they  consist  of  a  lower  mem- 
ber of  2500  to  2800  feet  of  dull-drab,  bluish  and  brown  shales  and  sand- 
stone interbedded  with  many  coal  seams.  The  upper  member  is  sub- 
divided into  the  Tongue  River,  Intermediate  and  Ulm  coal-bearing 
groups.  The  sandy  beds  are  in  many  places  only  slightly  consoli- 
dated. In  the  Tongue  group  which  is  about  800  feet  thick  there  are 
at  least  seven  seams  ranging  from  5  to  32  feet  in  thickness.  The 
Ulm  group  is  900  to  1150  feet  thick  and  there  is  a  distinct  horizon- 
marker  in  the  lower  part  of  the  group  in  the  form  of  a  shell  bed  which 
in  some  places  is  directly  overlain  by  a  coal  seam  and  in  other  places 
separated  from  it  by  30  to  40  feet  of  sand.  There  are  two  workable 
beds  in  this  group,  the  Arvade,  5  to  10  feet  thick,  and  the  Felix, 
6  to  30  feet  thick.  The  Ulm  group  contains  the  Lower  Ulm  or  Healy 
bed,  10  to  1 5  feet  thick.  The  coal  is  all  lignite  and  is  used  for  domestic 
purposes,  steam,  and  producer  gas.  The  structure  of  the  basin  is 
very  simple  and  the  beds  lie  almost  horizontal. 

The  main  mining  centers  of  the  state  are  in  Uinta  and  Sweet- 
water  counties.  These  areas  furnish  medium-grade  bituminous  coal. 
Subbituminous  coal  is  mined  in  Sweetwater,  Carbon,  Sheridan,  Con- 
verse, and  Bighorn  counties. 

The  coals  of  Wyoming  vary  in  age  from  Lower  Cretaceous,  of  the 
Kootenay  series  in  the  Black  Hills  region,  through  the  Mesaverde 
formation  in  the  Montana  series  of  the  Upper  Cretaceous,  to  the 
Fort  Union  of  the  Eocene.  The  older  coals  are  of  much  higher  grade, 
as  a  rule.  At  Cambria  a  bituminous  coal  is  mined  from  the  Lower 
Cretaceous  rocks.  In  the  Bighorn,  Wind  River,  Hams  Fork,  and 
Green  River  regions  the  coals  are  of  Upper  Cretaceous  (Montana 
and  Laramie)  and  Eocene  age.  They  vary  from  lignite  through 
subbituminous  to  bituminous  and  are  non-coking.  They  are  used 
for  domestic  purposes,  steaming  and  producer  gas. 

North  and  South  Dakota.1  —  North  Dakota  probably  has  the 
largest  reserve  of  coal  of  any  state  in  the  Union.  The  coal  of  the 
Dakotas  is,  however,  all  lignite.  It  is  estimated  that  nearly  35,000 
square  miles  in  North  Dakota  and  11,000  in  South  Dakota  are  un- 
derlain with  coal-bearing  beds  and  that  North  Dakota  contains  633,- 

1  U.  S.  Geol.  Survey,  22nd  Annual  Kept.,  Pt.  Ill,  p.  456.  Also,  Bulls.  285,  341,  381, 
471,  and  531. 


394 


THE   COAL   FIELDS  OF  THE   WORLD— AMERICA 


329,800,000  tons  of  lignite.  The  coal  is  almost  entirely  in  the  Fort 
Union  beds  of  the  Eocene.  The  beds  run  as  high  as  30  feet  in  thick- 
ness and  many  of  them  are  continuous  for  many  miles.  The  Lance 
formation  contains  a  little  coal,  but  in  most  places  the  seams  are  too 
thin  to  work.  The  latter  formation  does  not  appear  in  the  northern 
part  of  North  Dakota  but  is  extensively  distributed  around  the  border 


FIG.  134.  —  Lignite  seam,  Williston,  N.  Dak.     (After  F.  Wilder,  photo.     Reprinted  by 
permission  from  Ries'  Economic  Geology,  published  by  John  Wiley  &  Sons,  Inc.) 

between  the  Dakotas.  The  lignite  is  mined  only  along  the  main 
lines  of  the  railroad's  and  chiefly  for  domestic  purposes,  steaming 
and  producer  gas. 

Montana.1  —  This  state  contains  extensive  coal  lands.  The  Fort 
Union  Basin  of  the  Dakotas  extends  into  this  state  and  contains 
over  half  as  much  lignite  as  North  Dakota  in  nearly  the  same 
area.  The  other  areas  in  Montana  are  the  Bull  Mountain  field, 
the  Assinniboine  region,  the  Judith  Basin  region,  the  Flathead  River 
field,  the  Mountain  fields,  the  Yellowstone  region  and  the  Red  Lodge- 
Bridger  field.  The  Bull  Mountain  field,  which  is  being  developed, 
contains  rocks  of  Fort  Union  and  Laramie  age  or  slightly  older.  The 

1  U.  S.  Geol.  Survey,  22nd  Annual  Rept.,  Pt.  Ill,  p.  460.  Also,  Bulls.  316,  341,  356 
(Great  Falls  Field)  381, 531, 647  (Bull  Mountain),  University  of  Montana,  Bull.  4,  by  Rowe. 


CALIFORNIA  395 

structure  of  the  synclinal  basin  is  simple.  The  coal  varies  from 
lignite  in  the  Tertiary  rocks  to  subbituminous  and  low-grade  bitu- 
minous in  the  older  formations.  There  are  20  seams  over  2  feet 
thick  and  the  "  Mammoth  "  seam  runs  from  8  to  15  feet. 

The  field  which  is  most  largely  worked  is  the  Red  Lodge-Bridger 
field  where  coal  has  been  mined  for  a  good  many  years.  There  are 
seven  seams  running  from  3  to  12  feet  in  thickness.  The  coal  is 
high-grade  subbituminous,  fairly  high  in  moisture,  and  it  soon  breaks 
down  or  "  slacks  "  when  exposed  to  the  air. 

The  Great  Falls  field  in  Cascade  County,  forming  part  of  the 
Judith  Basin  region,  produces  considerable  coal  at  Sand  Coulee, 
Stockett  and  Belt.  The  coal  is  bituminous  and  dirty  and  it  occurs 
in  the  Kootenay  series  of  the  Lower  Cretaceous.  The  seams  in  some 
places  reach  nearly  15  feet  in  thickness.  The  North  Fork  Flathead 
River  field  is  considered  to  contain  unimportant  bituminous  and  sub- 
bituminous  coals  of  Jurassic  age  as  well  as  the  Cretaceous  coals.  The 
Assinniboine  region  is  represented  by  the  Milk  River  Field.  The 
strata  belong  chiefly  to  the  Montana  group  and  are  buried  under 
glacial  drift.  All  the  coal  in  this  field  occurs  in  the  Judith  River 
formation  of  the  Montana  series  except  a  little  lignite  in  the  Fort 
Union.  The  coal  beds  are,  as  a  rule,  lenticular  and  they  run  up  to 
9  feet  in  thickness.  Faults  and  folds  are  common  in  this  region. 
The  coal  is  of  fairly  good  subbituminous  grade.  In  many  areas  in 
this  state,  as  in  the  other  western  states,  the  coal  beds  have  been 
burned,  leaving  slag  and  reddened  rock.  This  is  partly  due  to  the 
ease  with  which  the  coal  ignites. 

The  Pacific  Coast  Province1 

California.2  —  The  coal  fields  of  California  are  very  limited  and 
there  is  no  prospect  of  her  ever  becoming  a  great  coal-mining  state. 
The  fields  are  also  widely  scattered,  the  main  ones  being  as  follows: 
lone  Mine  in  Amador  County,  Mount  Diablo  of  Contra  Costa  Coun- 
ty, Coral  Hollow  of  Alamada  County,  Priest  Valley  and  Trafton  of 
San  Benito  County,  and  Stone  Canyon  of  Monterey  County.  The 

1  Smith,  G.  O.,  The  coal  fields  of  the  Pacific  Coast.    U.  S.  Geol.  Survey,  22nd  Annual 
Kept.,  Pt.  Ill,  p.  473,  1902. 

2  Campbell,  M.  R.,  Coal  of  Stone  Canyon,  Monterey  County.    U.  S.  Geol.  Survey, 
Bull.  316,  p.  435,  1907- 


396  THE     COAL   FIELDS   OF   THE   WORLD— AMERICA 

coal  in  Stone  Canyon  is  of  bituminous  rank  with  a  composition 
approaching  cannel.  A  bed  10  to  14  feet  thick  has  been  exploited. 

The  coals  in  the  southern  part  of  the  state  are  bituminous  and  non- 
coking;  those  in  the  northern  part  are  lignite,  and  those  lying  be- 
tween these  fields  are  subbituminous.  Practically  the  only  coal  pro- 
duced in  the  state,  in  some  years  at  least,  is  lignite,  which  comes 
chiefly  from  the  lone  Mine,  Amador  County.  The  coal  is  of  Eocene 
and  Miocene  age.  The  coal  industry  of  all  the  western  states  where 
fuel  oil  is  found  in  abundance  is  vitally  affected  by  that  commodity 
and  will  continue  to  be  so  affected  as  long  as  oil  is  abundant. 

Oregon.1  —  Oregon  has  very  little  coal  and  comparatively  little 
mining  has  been  done.  In  the  Coos  Bay  field,  in  the  southern  part  of 
the  state,  mining  has  been  carried  on  and  coal  is  shipped  from  the 
Beaver  Hill  and  Newport  mines.  The  coal  is  subbituminous  in 
grade.  The  coal  in  this  field  is  difficult  to  mine  and  much  of  it  lies 
below  sea  level.  In  the  Eden  Ridge  field,  also  of  Coos  County, 
the  coal  is  bituminous  and  coking  as  the  strata  have  suffered  more 
squeezing  than  in  other  parts  of  the  county.  The  coal  is  shaly  and 
dirty.  A  number  of  other  small  fields  in  the  state  contain  thin  or 
impure  coal  seams,  but  there  is  no  development  in  these  fields.  The 
Oregon  coals  are  used  for  domestic  and  steaming  purposes. 

Washington.2  —  There  are  five  coal  fields,  confined  to  the  western 
and  central  parts  of  this  state.  They  are  the  North  Puget  Sound  in 
Skagit  and  Whatcom  counties,  South  Puget  Sound  in  Pierce  and  King 
counties,  Puget  Sound  basin  lying  just  east  of  Seattle,  the  Roslyn 
field  in  Kittitas  County  on  the  east  flank  of  the  Cascade  Mountains, 
and  the  Southwestern  field  in  Lewis  and  Cowlitz  counties. 

Washington  is  the  only  state  in  the  Pacific  province  containing 
coking  coals.  These  coals  are  in  the  North  and  South  Puget  Sound 
fields.  The  coals  of  this  state  range  from  subbituminous  rank  to 
anthracite.  Coal  has  been  mined  in  Washington  since  about  1860, 
the  first  mined  being  lignite,  but  spontaneous  combustion  closed  oper- 
ations. The  bituminous  coals  are  used  chiefly  on  the  ocean-going 
ships  and  the  subbituminous  for  domestic  purposes. 

1  Diller,  J.  S.,  Coos  Bay  Coal  Field.    U.  S.  Geol.  Survey,  igth  Annual  Rept.,  p.  309, 
1899. 

2  Washington  Geol.  Survey,  Vol.  II  and  Bull.  3.    Also  U.  S.  Geol.  Survey,  Bulls.  531 
and  541. 


ALASKA  397 

The  coals  in  King  County  lie  under  a  heavy  mantle  of  glacial 
drift.  They  are  of  Eocene  age,  like  the  other  coals  of  the  state, 
but  owing  to  the  compression  which  they  have  suffered  in  mountain 
building  they  have  been  changed  from  lignite  to  subbituminous  and 
bituminous  rank.  In  this  county  the  beds  have  been  highly  folded 
and  broken  so  that  in  parts  of  the  field  mining  is  difficult.  The 
ash  in  the  coal  is  high.  Pierce  County  carries  the  best  coals  in  Wash- 
ington so  far  as  known,  as  coals  are  bituminous,  semibituminous 
and  even  anthracite  where  the  rocks  have  been  highly  squeezed, 
broken  and  intruded  by  igneous  rocks.  The  bituminous  coals  will 
coke. 

In  the  Roslyn  field  the  beds  lie  regularly,  and  it  is  easy  to  mine 
the  Roslyn  seam,  running  between  2  and  3  feet  thick.  There  is 
also  another  seam  known  as  the  "  Big  "  seam  which  is  full  of  part- 
ings and  very  dirty.  It  reaches  nearly  20  feet  in  thickness.  The 
coal  is  bituminous. 

The  Puget  Sound  field  is  characterized  by  the  tremendous  number 
of  coal  seams  which  the  formations  contain.  In  one  place  there 
are  about  125  seams,  the  majority  of  which  are  unworkable.  This 
indicates  a  great  number  of  changes,  probably  rapid  ones,  in  the 
climatic  or  topographic  conditions,  or  both,  during  the  formation 
of  these  beds. 

Alaska1 

The  coal  fields  of  Alaska  are  but  partially  known,  as  so  little  ge- 
ological work  has  been  done  on  this  tremendous  area.  More  or 
less  work  has  been  done  on  certain  regions  and  fields,  and  a  rough 
estimate  of  the  character  of  the  coals  and  their  resources  may  be 
given.  The  accompanying  map  and  the  following  table  show  the 
geographical  and  geological  distribution  of  the  coals,  so  far  as  known. 

The  following  fields  or  areas  are  recognized:  Bering  River,  Matan- 
uska,  Cook  Inlet,  Alaska  Peninsula,  Nenana,  Northern  Alaska  and 
many  other  less-known  fields  and  areas. 

1  Brooks,  Alfred  H.,  and  Martin,  George  C.,  Coal  resources  of  the  world.  Inter- 
national Geological  Congress,  Vol.  II,  1913.  U.  S.  Geol.  Survey,  22nd  Annual  Rept., 
Pt.  Ill,  p.  515,  1902;  and  Bulls.  284  and  314. 


398  THE   COAL   FIELDS  OF  THE  WORLD— AMERICA 

STRATIGRAPHIC  POSITION   OF  ALASKAN   COALS* 


System 

Series 

Character  of  coal 

Principal  distribution 

Quaternary 

Pleistocene 

Lignitic 

Yukon      basin      and 

other    parts    of    Al- 

aska. 

Pliocene 

Lignitic 

Yakutat      Bay     and 

other  localities. 

Tertiary 

Miocene  or  Eocene 

Anthracitic    and    bi- 

tuminous.      Chiefly 

Bering  River. 

Eocene 

lignitic,     also    some 
bituminous  and  sub- 

Throughout     Alaska, 
notably  on  Cook  In- 

bituminous 

let,     in    Matanuska 

Valley    and    Yukon 

Basin. 

Cretaceous 

Upper  Cretaceous 

Subbituminous      and 

Alaska  peninsula,  Yu- 

bituminous 

kon     and      Colville 

basins. 

Jurassic 

Lignitic,     subbitumi- 

Near   Cape   Lisburne 

nous  and  bituminous 

and    in    Matanuska 

Valley. 

Carboniferous 

Pennsylvanian 

Subbituminous 

Yukon  River. 

Mississippian 

Bituminous 

Twenty   miles    south 

of   Cape    Lisburne. 

'  Table  by  A.  H.  Brooks  and  G.  C.  Martin,  Coal  Resources  of  the  World. 

The  Bering  River  is  an  important  field  lying  25  miles  northeast 
of  Controller  Bay.  The  coal  beds  run  from  3  to  25  feet  in  thickness, 
in  the  Kustaka  formation  which  is  about  2000  feet  thick  and  of 
Miocene  age.  The  field  is  greatly  folded  and  faulted  and  in  many 
places,  especially  in  the  eastern  and  western  ends  of  the  field,  the 
coal  beds  are  so  badly  crushed  as  to  ruin  the  coal.  The  coals  vary 
from  anthracite,  averaging  about  81  per  cent,  to  semibituminous 
with  72  per  cent  fixed  carbon.  Some  of  the  bituminous  coal  will 
coke. 

Another  important  field  is  the  Matanuska,  lying  along  the  valley 
of  the  Matanuska  River,  about  25  miles  from  Knik-Arm.  The 
measures  are  deeply  covered  with  gravel  in  parts  of  the  field.  The 
rocks  are  of  Eocene  age  and  in  the  eastern  part  of  the  field  highly 
folded  and  faulted.  It  is  probable  that  the  field  will  cover  about  100 
square  miles.  The  seams  range  from  3  to  32  feet  in  thickness.  In 
the  west  end  of  the  field  the  coal  is  lignite  and  in  passing  eastward 
it  changes  to  bituminous  coal  and  anthracite.  Some  of  the  coal  is 
high  in  ash  but  the  average  content  is  favorable. 

In  the  Cook  Inlet  field  lignite  occurs  in  the  Kenai  formation  of 


ALASKA 


399 


the  Eocene.  There  are  fifteen  or  more  seams  running  from  3  to  7 
feet  in  thickness.  On  the  Alaska  Peninsula  lignite  occurs  in  the 
Kenai  formation,  but  better  coal  is  found  in  the  Chignik  formation  of 
the  Upper  Cretaceous  around  Chignik  Bay  and  Herendeen  Bay.  In 
this  formation  the  coal  is  subbituminous  and  bituminous  of  fair 
quality,  but  little  is  known  of  the  extent  of  the  seams. 


LEGEND 

COAL  AREAS  AND  THEIR 
POSSIBLE  EXTENSION 

SMALLER  COAL  AREAS  " 

AREAS  KNOWN  TO  CONTAII 
ANTHRACITE  AND  HIGH 
GRADE  BITUMINOUS  COAL 
AREAS  THAT  MAY  CONTAIN 
ANTHRACITE  AND  HIGH 
GRADE  BITUMINOUS  COAL 


[AREAS  KNOWN  TC 
L       [LIGNITE 


FIG.  135.  —  Alaska,  showing  distribution  of  coal  deposits.  (After  A.  H.  Brooks. 
Reproduced  from  "Coal  Resources  of  the  World."  Published  by  the  1 2th  Interna- 
tional Geological  Congress,  Toronto,  Canada.) 

In  Northern  Alaska  there  are  three  coal-bearing  formations:  one 
is  Carboniferous,  supposedly  Mississippian,  containing  high-grade 
bituminous  coals  with  low  ash  content;  another  is  Jurassic  with  a 
large  number  of  beds  of  subbituminous  coal  running  as  high  as  1 2 
feet  in  thickness;  and  the  third  is  Tertiary,  carrying  lignite.  The 
older  beds  are  considerably  folded  and  faulted  but  those  in  the  Ter- 
tiary are  quite  flat. 

In  the  Nenana  field  there  are  a  number  of  beds  running  from  3 
to  30  feet  in  thickness.  They  occur  in  the  Eocene,  and  the  coal 
is  mostly  lignite. 


400 


THE   COAL   FIELDS  OF  THE  WORLD— AMERICA 


The  table  given  below  is  a  summary  of  the  estimates  of  Brooks 
and  Martin  for  the  coal  fields  of  Alaska,  in  so  far  as  information  is 
available. 

ESTIMATE  OF  TONNAGE  OF  COAL  IN  ALASKA* 


Regions 

Area  in 
square  miles 

Estimated  amount  of  coal  in  metric  tons 
(i  metric  ton  =  1.1023  short  tons) 

Total 

Known 
coal  fields 

• 
<u  % 

|«S 

n 

Lignite 

Sub- 
bituminous 

Bitumi- 
nous 

Semibitu- 
minous 

Anthracite 
and 
semianthra- 
cite 

Pacific  Coast.. 
Interior  Region 
Arctic  Slope... 

458 
440 
312 

8,585 

4,493 
3,059 

1,971,000,000 
9,731,000,000 
910,000,000 

485,000,000 
53,000,000 
3,143,000,000 

2,000,000 

14,000,000 

1,293,000,000 
60,000,000 

1,931,000,000 

5,682,000,000 
9,798,000,000 
4,113,000,000 

Totals 

1,210 

16,137 

12,612,000,000 

3,681,000,000 

16,000,000 

1,353,000.000 

1,931,000,000 

19,593.000,000 

*  This  estimate  is  based  on  seams  3  feet  or  more  in  thickness  and  lying  less  than  3000  feet  deep  for  high- 
grade  coal  (anthracite  to  semibituminous),  and  less  than  2000  feet  deep  for  lower  grades  (bituminous  to  lignite). 

MEXICO 

The  coals  of  Mexico  are  but  little  developed.  Only  one  state 
produces  any  quantity  and  submits  regular  reports  of  production. 
There  are  several  regions,  according  to  R.  T.  Hill1,  which  contain  coal, 
and  the  coals  are  of  three  geological  ages:  Tertiary,  Upper  Creta- 
ceous and  Triassic.  The  Tertiary  lignites  represent  a  continuation 
of  the  deposits  of  that  age  in  the  United  States,  but  so  far  as  known 
they  are  of  no  importance  in  Mexico.  The  Triassic  coals  occur  in 
two  districts,  the  Mixteca  district  in  the  south  where  there  are  a 
large  number  of  seams  of  workable  thickness  but  too  high  in  ash 
to  be  valuable,  and  the  Santa  Clara  field  where  the  coal  is  semi- 
anthracite  and  anthracite  because  it  has  suffered  much  from  com- 
pression and  igneous  intrusions.  Natural  coke  and  graphite  in  suffi- 
cient quantity  to  be  mined  have  resulted  from  these  disturbances. 
The  seams  run  4,  8  and  10  feet  in  thickness. 

The  producing  fields  are  all  Montana  (Upper  Cretaceous),  in  age 
and  they  occur  in  Coahuila.  They  are  known  as  the  Eagle  Pass, 
Sabinas  and  Barroteran  fields.  There  is  a  small  production  from 

1  Hill,  Robert  T.,  The  coal  fields  of  Mexico.  Coal  Resources  of  the  World,  Vol.  II, 
P-  553- 


WEST  INDIES  401 

the  Eagle  Pass  field,  which  is  situated  in  the  vicinity  of  Eagle  Pass, 
Texas  and  Porfirio  Diaz  in  Mexico.  This  field  is  a  continuation  of 
the  field  of  the  same  name  in  Texas.  In  the  Sabinas  field  there 
are  two  beds  4  to  6  feet  thick,  of  good,  coking,  bituminous  coal. 
A  clay  seam  between  the  beds  causes  some  difficulty  in  working. 
The  Barroteran  field  is  a  continuation  of  the  Sabinas  field  along 
the  north  side  of  the  Santa  Rosa  Mountains.  In  this  field  the 
seam  is  8  feet  thick  with  14  inches  of  clay  and  shale  and  it  is  regular 
and  persistent.  The  coal  is  bituminous  and  coking.  A  number  of 
American  companies  are  working  mines  in  Mexico  in  the  Sabinas 
and  Barroteran  fields  and  a  considerable  number  of  coke  ovens  are 
in  operation. 

CENTRAL  AMERICA1 

The  only  countries  in  Central  America  reporting  any  coal  re- 
sources are  Honduras  and  Panama.  The  former  country  reports 
5,000,000  metric  tons,  all  lignite  except  about  1,000,000  tons  of 
bituminous  coal  in  the  district  of  El  Paraiso.  The  beds  run  from  i 
foot  6  inches  to  4  feet  in  thickness,  but  they  have  never  been  mined. 
Panama  has  a  little  lignite  in  the  province  of  Bocas  del  Toro  on  the 
coast  and  in  the  interior.  That  on  the  coast  is  largely  submarine 
and  under  porous  strata  while  that  in  the  interior  is  too  high  in  sul- 
phur to  be  valuable.  It  is  interesting  to  note  that  the  sulphur  is 
said  to  increase  as  the  volcano  Chiriqui  is  approached. 

WEST  INDIES 

Cuba  has  no  coal  and  the  only  resources  reported  for  the  West 
Indies  are  found  in  Trinidad.  The  coal  has  not  been  exploited, 
but  there  are  two  districts  in  which  it  is  known  to  occur.  These 
are  near  Manzanilla  and  Sangre  Grande  on  the  east  coast.  In  the 
former  area  the  coal  is  lignite,  the  seams  thin,  not  exceeding  4  feet, 
and  the  deposit  is  poor  in  quality.  In  the  Cunapo  district,  near 
Sangre  Grande  prospects  are  a  little  better.  There  are  two  seams 
of  subbituminous  coal,  one  of  which  is  5  feet  thick  and  can  be  traced 
fcr  a  considerable  distance,  but  they  lie  on  an  irregular  bottom  and 
are  probably  not  of  much  importance. 

1  Coal  Resources  of  the  World. 


402  THE   COAL   FIELDS  OF  THE  WORLD— AMERICA 

South  America 

South  America  is  apparently  deficient  in  good  coal  deposits,  and 
very  little  definite  information  has  been  collected  on  her  coal  re- 
sources as  the  best  available  data  place  her  actual  reserve  at  2,089,- 
000,000  metric  tons  and  her  probable  reserve  at  32,010,000,000  tons. 
The  geological  ages  of  the  coals  are  Permo-Carboniferous,  Creta- 
ceous and  Tertiary,  (Plate  XV).  The  following  countries  are  reported 
to  carry  at  least  some  coal:  Colombia,  Venezuela,  Ecuador,  Peru, 
Bolivia,  Argentina,  Brazil  and  Chile.  The  coals  vary  from  anthra- 
cite to  lignite  in  character. 

Colombia.1  —  Coal  is  found  in  several  departments  of  the  country, 
but  worked  in  few.  Mines  are  operated  in  the  vicinity  of  Bogota  in 
the  Departments  of  Cundinamarca  and  in  Boyaca  and  to  a  lesser  ex- 
tent in  the  Department  of  Antioquia.  The  coal  is  bituminous  and 
most  of  it  is  used  locally  for  railroads,  and  for  domestic  and  metal- 
lurgical purposes.  According  to  Gamba  the  largest  fields  are  in 
the  districts  of  Cauca  and  Valle  where  there  are  three  seams  of  medi- 
um-grade bituminous  coal,  with  an  aggregate  thickness  of  6  feet 
6  inches  and  estimated  resources  of  20,000,000,000  metric  tons  in 
seams  over  i  foot  thick  and  less  than  3000  feet  deep.  Little  or  no 
mining  has  yet  been  done  in  these  departments.  The  Departments 
of  Cundinamarca  and  Boyaca  have  the  same  number  of  seams  with 
the  same  aggregate  thickness  of  coal  and  resources  of  6,000,000,000 
metric  tons.  The  same  number  of  seams  with  the  same  aggregate 
thickness  contain  1,000,000,000  metric  tons  in  Antioquia.  No  es- 
timate of  the  resources  of  the  Department  of  Narino  is  available, 
but  they  are  believed  to  be  very  large  as  there  is  supposed  to  be  a 
large  unstudied  field  in  the  vicinity  of  the  Putumayo  River.  These 
figures  make  a  total  estimate  of  twenty-seven  billion  tons  in  the 
best-known  fields.  Miller  and  Singewald2  quote  Ospma  as  saying 
that  in  the  western  coal  area  there  are  as  many  as  six  seams,  one 
as  much  as  Q|  feet  thick.  Most  of  the  coal  is  a  hard  compact  lignite 
except  where  it  has  been  subject  to  considerable  metamorphism.  Ap- 
parently this  coal  is  a  subbituminous  coal,  as  the  term  is  used  in  the 
United  States. 

1  Gamba,  F.  P.,  Coal  resources  of  Colombia.     Coal  Resources  of  the  World,  1913. 

2  Miller,  B.  L.,  and  Singewald,  J.  T.  Jr.,  Mineral  deposits  of  South  America,    p.  357, 
1919. 


CARIBBEAN 

SEA 


ritiba 
Alegre 
Pardo 
lota. 


Valparaiso  f^  ;Mendoza 

Santiao    /  Buenos  Ai 

Conce 
Cuiri«uina»  ni/       San  Rafael 


SOUTH  AMERICA 


3CALE  OF  MILES 

0  200         400 

800  Statute  Miles  to  1  Inch 


Capitals    •-.'  Other  Cities 

Mesozoic  Coals 
Paleozoic  Coals 


Longitude 


from       60° 


Greenwich 


PLATE  XV.  — Coal  fields  of  South  America.  (Reproduced  from  "Coal  Resources  of 
the  World,"  published  by  the  i2th  International  Geological  Congress,  Toronto, 
Canada). 

(403) 


404  THE   COAL  FIELDS  OF  THE  WORLD— AMERICA 

F.  Lynwood  Garrison1  mentions  some  peculiar  coal  from  Ca- 
cagual  on  the  Taraza  River.  There  are  several  seams  varying  from 
a  few  inches  to  5  feet.  The  coal  is  compact  and  glassy  and  it  re- 
sembles cannel.  It  possesses  a  distinctly  laminated  structure  and 
it  can  be  lighted  with  a  match.  It  burns  with  a  glow  like  punk  and 
not  with  a  long  flame  as  cannel  does.  This  coal  has  the  pe- 
culiarity of  being  overlain  by  rich  gold-bearing  gravels.  Analyses 
show  its  composition  to  be  as  follows:  Moisture,  13.6  to  15.36; 
Volatile  matter,  38.10  to  47.41;  Fixed  carbon,  44.40  to  32.67;  Ash, 
3.80  to  4.56  and  Sulphur,  0.54  per  cent.  Garrison  also  quotes  anal- 
yses by  Percy  which  show  coals  from  Colombia  with  oxygen  and 
nitrogen  combined  varying  from  12.06  to  22.12  per  cent. 

The  better  coals  of  Colombia  are  of  Upper  Cretaceous  age.  There 
is  considerable  lignite  of  Tertiary  age,  but  little  is  known  regard- 
ing it. 

Venezuela.  —  According  to  Miller  and  Singewald2  coal  is  widely 
distributed  in  Venezuela  north  of  the  Apure  and  Orinoco  rivers  and 
the  Llanos.  The  age  is  doubtful,  probably  Cretaceous  and  Tertiary. 
All  the  coals  are  lignites  or  subbituminous  except  for  one  area  of 
semianthracite.  There  are  numerous  seams,  the  thickest  reported 
running  up  to  about  10  feet.  Some  of  the  areas  in  the  Balcelonia 
district  have  been  highly  folded. 

Ecuador,  Peru,  Bolivia.  —  Ecuador  does  not  report  any  operating 
coal  mines  but  this  country  has  a  little  coal  of  good  quality,  varying 
from  lignite  to  anthracite.  The  places  so  far  mentioned  are  at 
Cojitambo,  Mangan  and  Biblian  in  the  province  of  Cafiar.  Anthra- 
cite occurs  at  San  Antonio  de  Pomasqui,  north  of  Quito.  It  is  of 
Tertiary  age. 

Peru  has  rather  extensive  coal-bearing  areas  running  through  the 
Andes  Mountains.  The  quality  of  the  coal  varies  from  low-grade 
bituminous  to  anthracite.  Her  resources  have  been  placed  at  ap- 
proximately two  billion  tons,  of  which  seven  hundred  million  are 
anthracite  and  semianthracite.  The  age  of  the  coal  is  Cretaceous 
or  Tertiary.  According  to  Borlkjof3,  anthracite  containing  from  84 
to  87  per  cent  fixed  carbon,  occurs  in  Cajabamba  province,  and  in 

1  Garrison,  F.  Lynwood,  Mining  and  Scientific  Press.     Vol.  98,  p.  219,  1909. 

2  Op.  cit.,  p.  542. 

3  Borlkjof,  J.  Camilo  B,  The  coal  deposits  of  Peru.     Eng.  and  Min.  Jour.,  Vol.  88, 
p.  983,  1919. 


ARGENTINE   REPUBLIC  405 

Chota,  about  140  miles  from  the  Pacific,  there  are  four  anthracite 
beds  from  13  to  65  feet  thick.  There  is  estimated  to  be  700,000,000 
tons  of  coal  in  this  area.  There  is  a  large  amount  of  coal  in  the  Depart- 
ment of  Lima  and  in  the  Province  of  Chamcay,  at  Checras.  In  the 
provinces  of  Parquin  and  Quiruragra  there  is  a  bed  which  reaches  a 
thickness  of  13  feet  and  the  resources  are  estimated  at  720,000,000 
tons.  This  is  the  largest  and  most  important  field  in  Peru.  It  is  situ- 
ated near  the  Cerro  de  Pasco  copper  camp  and  coal  is  being  mined  by 
this  company.  A  number  of  coal  mines  are  worked  in  Peru,  some 
of  them  being  highly  gaseous.  It  seems  probable  that  Peru  will  be 
found  to  contain  much  larger  reserves  than  those  mentioned  above 
and  that  she  will  be  quite  an  important  producer  of  high-grade  coal 
in  the  future. 

Practically  nothing  is  known  regarding  the  coal  deposits  in  Bolivia 
beyond  the  fact  that  they  seem  to  be  of  small  importance  and  to 
be  Permo-Carboniferous  in  age.  A  few  outcrops  of  impure  seams 
occur  on  Lake  Titicaca  but  little  work  has  been  done  on  them.  The 
inhabitants  of  that  country,  most  of  which  lies  at  an  elevation  of 
over  8000  feet  above  sea  level,  suffer  a  great  deal  from  cold  owing 
to  the  great  altitude  and  the  scarcity  of  fuel. 

Brazil.  —  A  number  of  coal  mines  have  been  operated  from  time 
to  time  in  Brazil,  but  so  far  very  little  coal  sufficiently  free  from 
slate  and  low  enough  in  sulphur  and  ash  to  make  a  good  industry 
has  been  found.  The  extensive  report  of  I.  C.  White1  shows  that 
only  by  laborious  picking,  washing  and  briquetting  can  a  satisfactory 
fuel  be  obtained.  The  most  favorable  localities  are  in  the  south 
near  the  Uruguay  border.  The  coal  occurs  in  the  Rio  Bonita  beds 
of  the  lower  Permian  which  are  correlated  with  the  lower  Karroo 
of  South  Africa. 

Argentine  Republic.  —  No  coal  deposits  of  importance  have  been 
found  in  this  great  country.  Thin  seams  are  found  in  a  number 
of  places,  as  the  Permo-Carboniferous  rocks  outcrop  along  the  eastern 
border  of  the  Andes  and  a  seam  has  in  recent  years  been  exploited 
at  Salagasta  in  the  province  of  Mendoza.  It  is  reported  that  a 
seam  10  to  12  feet  thick  was  struck  at  a  depth  of  about  2000  feet. 
The  coal  is  fairly  low-grade  bituminous.  In  Mendoza  there  are 

1  Final  Report  of  I.  C.  White,Chief  of  the  Brazilian  Coal  Commission,  Rio  Janiero,  1908. 


400  THE  COAL  FIELDS  OF  THE  WORLD— AMERICA 

some  beds  of  Albert! te  which  somewhat  resembles  coal  but  is  a  solid 
derived  from  petroleum. 

Chile.1  —  There  are  two  provinces  in  Chile  which  contain  coal 
fields  of  importance  and  in  which  coal  is  being  worked.  These 
are  Arauco  and  Concepcion.  In  the  former  the  places  where  mines 
are  worked  are  Maquehua,  Arauco,  Pilpilco  Cuyinco,  and  Lebu 
and  in  the  latter  Penco,  Lirquen,  Coronel  and  Lota.  The  seams 
worked  vary  in  thickness  from  0.70  meter  to  1.85  meters.  At  Coro- 
nel eight  seams  are  mined  and  at  Arauco  six  seams.  In  the  Penco 
district  the  coal  is  mined  to  a  considerable  extent  beneath  the  sea. 
The  strata  are  little  folded  as  a  rule  but  normal  faults  are  fairly 
numerous.  The  age  of  most  of  the  Chilian  coal  is  Tertiary,  probably 
Oligocene  or  Miocene,  and  it  is  of  bituminous  rank;  much  of  it  being 
of  inferior  quality.  The  coal  resources  of  Chile  are  estimated  at 
2,082,000,000  metric  tons. 

1  Michado,  Miguel  R.,  Le  Charbon  du  Chili  et  sa  Distribution  Geographique.  Coal 
Resources  of  the  World,  Vol.  II,  p.  581. 


» 


J 


COAL  AREAS  OF  EUROPE  * 


A  AAh^Syt'  vpBe/[  r  J    ^    ^\   , 

S^wl  &{t*£>, ( X 

Sary.*  ^tr^tJ  "X-v 


PLATE  XVI. —  The  Coal  fields  of  western  Europe.    (Reproduced  from  "Coa 

Toroni 


:es  of  the  World."     Published  by  the  i2th  International  Geological  Congress, 


: 


CHAPTER  XIV 

THE   COAL   FIELDS   OF   THE   WORLD  —  EUROPE 
AND    ASIA 

Europe1 

Europe  was  the  mother  of  the  coal-mining  industry,  which  still 
flourishes  on  that  continent,  although  in  some  respects  America 
has  surpassed  her  in  the  development  of  mining  operations.  Al- 
though her  resources  are  small  compared  with  those  of  America, 
Europe  is  well  supplied  with  high-grade  coal  and  she  is  more  careful 
to  utilize  a  greater  proportion  of  it  than  we  have  been  in  America. 

The  table  given  below  shows  the  actual  and  estimated  resources 
of  coal  in  the  various  countries  of  the  continent  and  the  accompany- 
ing maps  picture  the  area  and  distribution  of  the  coal  fields  (Plates 
XVI  and  XVII.) 

This  table  indicates  that  the  German  Empire  controls  by  far  the 
largest  coal  resources  of  the  countries  of  Europe.  Great  Britain 
comes  second,  Russia  in  Europe  third,  Austria  fourth  and  France 
fifth.  Italy  has  almost  no  coal  in  comparison  with  her  population. 
Russia  has  a  large  estimated  tonnage  of  anthracite  —  almost  twice 
that  of  the  United  States  and  second  only  to  China.  The  figures 
given  for  Roumania  do  not  properly  indicate  her  probable  reserves. 
The  annual  production  of  European  countries  is  given  on  page  335. 

Great  Britain.2  —  Great  Britain  has  long  been  one  of  the  leading 
coal-producing  states  of  the  world  and  she  is  surpassed  in  production 

1  For  comprehensive  descriptions  of  the  coal  deposits  of  Europe  see  Atlas  general  des 
Houilleres  (Text  and  Atlas)  by  E.  Gruner  et  G.  Bousquet,  Comite  Central  des  Houil- 
ISres  de  France,  Paris,  1911.     Also  Coal  Resources  of  the  World,  International  Geological 
Congress.    Vol.  I. 

2  For  comprehensive  reports  see  the  Coal  Resources  of  Great  Britain  by  A.  Strahan, 
Coal  Resources  of  the  World.    Also  various  Memoirs  of  the  Geological  Survey  of  England 
and  Wales  on  individual  fields.     Analyses  of  British  Coals  and  Coke  and  the  Character- 
istics of  the  Chief  Coal  Seams  worked  in  the  British  Isles,  by  Greenwell  and  Elsden. 
Colliery  Guardian,  London,  1907.    Reports  of  the  Royal  Commission  on  Coal  Supplies, 
1905. 

407 


408       THE   COAL   FIELDS  OF  THE   WORLD— EUROPE  AND   ASIA 


*COAL  RESOURCES   OF   EUROPE   IN  MILLIONS   OF   METRIC   TONS 
(i  metric  ton  =  1.1023  short  tons) 


Actual  Reserve 

Probable  Reserve 

Total 

Class  of  Coal 

Class  of  Coal 

A 

BandC 

D 

A 

BandC 

D 

Anthra- 
cite in- 
cluding 
some  dry 
coals 

Bitumi- 
nous coals 

Subbitu- 
minous 
coals, 
brown 
coals  and 
lignites 

Great  Britain  and  Ireland: 
England         

8,672 
2,500 
172 

B    79,869 
B    31,402 
B    18,876 
B            8 

13 

B    46,030 
B         195 
B      1,685 
B        in 

Wales    

Scotland      .   

Ireland  

Portugal              

11,344 
20 

1,008 
42 

130.155 

B     2,016 
C     2,016 
B        358 
C        386 

394 

13 

148 
437 

48,021 

B        296 
C        296 
B         567 
C         431 

373 

189,533 

20 

Spain: 
Asturias      

Other  fields  

France: 
North  of  Ardennes  Massif.  . 

Eastern  
Armorican  Massif  

1,050 
520 

59 

2 

4,776 

B      2,600 
C        670 
B            3 

B               2 

B        233 
C        114 

394 
301 

585 
1,690 

7 
890 

103 

1,590 

B      6,260 
C        420 
B          13 
C        630 
B          24 
B      1,079 
C        632 

373 
1,331 

8,768 

Central  Massif  

Alps  

Lignite  areas 

Italy  

581 

I 

SO 

3,622 
159 

301 
51 

10 

2,690 
143 

270 

9,058 

C         30 
3,923 

B     7,oco 
B     1,000 
B     3-ooc 

i,33i 

48 
30 
358 
50 

17,583 

243 
40 
388 
50 
4,402 

Greece  

Bulgaria  

Denmark  (Faroes)  

Netherlands 

Belgium 

Campine: 
Limburg 

D'Anveres  

Namur  

11,000 

11,000 

EUROPE 
COAL  RESOURCES  OF  EUROPE    (Continued) 


409 


• 

Actual  Reserve 

Probable  Reserve 

Class  of  Coal 

Class  of  Coal 

Total 

A 

BandC 

D 

A 

BandC 

D 

Anthra- 
cite  in- 
cluding 
some    dry 
coals 

Bitumi- 
nous coals 

Subbitu- 
minous 
coals, 
brown 
coals  and 
lignite 

Germany: 
Saar  district     

16,548 
56,344 
B        718 
B    10,325 
B        225 
B    10,458 
B        247 

3,ooo 

6,069 
75 
169 

157,222 

B     2,226 
B  155,662 

3,676 
293 
99 

Westphalia         

L  Silesia      

U  Silesia  

Saxony            

Left  of  the  Rhine  

Other  districts  
North  German  States  

Hesse 

94,86s 
B            4 
B     2,970 

B               2 

B        106 
B          57 

9,313 
354 
12,231 

1,700 
58 
3 

12 

37,599 

315,110 
B        109 
B    38,012 

B          43 
B            8 
B     2,525 

B    18,014 

B        253 

4,068 
1,250 
663 
1,976 
426 
36 

1,578 
43 
25 

423,356 
i,7i7 
53,876 
3,676 
529 
39 
H4 

Bosnia  and  Herzegovina  
Servia             

Roumania  

Russia; 
Dombrova  (Poland)        . 

Donetz                      .   . 

S.  W.  Russia    

W.  Urals    

Caucasus  

B          57 

12 

37,599 

20,792 
8,750 

1,646 

60,106 
8,750 

Total  for  Europe  

13.046 

236,716 

24,427 

41,300 

456,446 

12,255 

784,190 

*  From  the  Coal  Resources  of  the  World.  Estimate  based  on  seams  more  than  I  foot  thick  and  less 
than  4000  feet  deep  and  on  seams  more  than  2  feet  thick  and  between  4000  and  6000  feet  in  depth.  For 
detailed  description  of  the  classes  of  coal,  see  Classification  of  Coals,  Chapter  V. 


410       THE   COAL  FIELDS  OF  THE   WORLD— EUROPE   AND   ASIA 


TABLE  SHOWING  THE  GEOLOGICAL  AGES  OF  EUROPEAN  COALS 


England  and  Wales 

Scotland 

Ireland 

Portugal 

c 

1 

1 

Switzerland 

2 

i 

SJ 

I 

.5 
1 

Denmark 

Netherlands 

S 

Germany 

Hungary 

Austria 

Bosnia-Herzegovina 

1 

Roumania 

Sweden 

Norway 

B 

"N 
'5. 

dS 

Russia  m  Europe 

Pleistocene  

Pliocene  

f 

, 

B 

B 

Oligocene 

B 

Eocene               .    . 

i 

. 

Tertiary  undifferen- 
tiated  

L 

L 

L 

B 

1 

L 

L 

L 

Upper  Cretaceous  

L 

L 

B 

- 

) 

L 

L 

Lower  Cretaceous  

Jurassic 

j 

p 

1 

Triassic  (Rhaetic)  

) 

1 

) 

) 

Permian  

Upper    Carboniferous 
(Pennsylvanian)  .  .  . 

A 
S 
B 

A 
S 
B 

i 
B 

a 

B 

B 

A 

i 

a 

B? 

a 
B 

a 

B 

A 
S 

B 

B 

B 

B 

3 

i 

a 

b 

b 

t 

B 

Sub-carboniferous  
(Mississippian)  

A 
S 
B 

B 

B 

A 

B 

B 

A 
Be 

Upper  Devonian  

1 

b 

A,  Anthracite  and  semianthracite;  S,  Semibituminous;  B,  Bituminous;  B,  Subbituminous;  L, 
Lignite.  Capital  letters  indicate  important  deposits  and  lower  case  relatively  unimportant  deposits  of 
the  same  type. 


GREAT  BRITAIN  41-1 

only  by  the  United  States.  She  has  given  us  many  of  our  mining 
methods  and  many  of  the  principles  involved  in  our  mining  apparatus 
as  well  as  a  wonderfully  efficient  and  hardy  class  of  mining  men. 
Her  coal  supplies  have  been  one  of  the  very  important  factors  in  the 
attainment  of  her  high  position  in  the  industrial  and  commercial 
world,  and  she  has  exported  coal  lavishly  to  those  countries  less 
favored  by  nature  in  coal  deposits  than  she.  The  tables  given 
above  show  that  she  is  exhausting  her  supplies  at  a  much  greater 
rate  in  proportion  to  her  resources  than  any  of  the  other  great  com- 
mercial countries  with  the  exception  of  France.  The  conclusion  of 
the  Royal  Commission  on  Coal  Supplies  in  iSyi1  was  that  there 
was  enough  coal  in  sight  to  continue  the  existing  rate  of  production 
for  1273  years,  but  that,  considering  the  probable  rate  of  increase 
in  production,  there  was  sufficient  coal  to  last  between  325  and  433 
years.  The  latter  figure  would  be  much  too  high  if  the  rate  of  in- 
crease should  continue  a  few  years  longer. 

Several  very  thorough  reports  have  been  prepared  on  the  coal 
resources  of  the  islands  and  the  available  supplies  are  very  well 
known.  The  fields  are  usually  divided  into  two  groups,  known  as 
(a)  the  Visible  and  Proved  fields;  and  (b)  The  Concealed  and  as 
yet  unworked  fields.  The  first  group  includes  those  fields  where 
the  Coal  Measures  are  not  deeply  buried  by  later  formations,  and 
the  second  group  those  fields  where  they  are  deeply  covered  but  where 
they  are  known  to  exist  in  synclinal  basins.  In  computing  the  re- 
sources it  was  assumed  that  a  thickness  of  i  foot  of  coal  represents 
960,000  tons  per  square  mile,  or  1500  statute  tons  per  acre.  The 
various  fields  with  the  number  and  thicknesses  of  the  seams,  the 
character  of  the  coal  and  the  resources  of  each  field  are  set  forth 
in  the  following  table  compiled  by  Strahan. 

1  Reports  of  the  Royal  Commission  on  Coal  Supplies,  1871  and  1905. 


412       THE    COAL   FIELDS  OF   THE   WORLD— EUROPE   AND   ASIA 


O  O 

g  O 

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CQPQPQ    «    pq 


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||l 

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s   ?8§S  S  a 

S 


O'MN 


PQ 

PQ     PQ    pq  PQ  pq  PQPQ 

pq    «<    pq'pq  pq  w  pq  pq  pq  pq  pq  pq  pq  pq  pq  pq  pqpq 

pq     <j  <j  pq  pq  pq  pq  pc ipq  pq  pq  pq  pq  pq  pq  pq  pq  pqpq 


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GREAT  BRITAIN 


413 


In  addition  to  the  totals  given  above  there  are  calculated  to  be 
6,207,847,000  metric  tons  of  actual  reserve  in  seams  running  over  2 
feet  in  thickness  and  lying  at  depths  between  4000  and  6000  feet. 

THE   COAL  RESOURCES   OF   SCOTLAND 
(Including  seams  of  i  foot  or  over  to  a  depth  of  4000  feet.) 


District 

Coal  Seams 

Actual  Reserve 
(Calculations  based  on  actual 
thickness  and  extent) 

No. 

Thickness 
(Aggregate) 

Area, 
sq. 
miles 

JClass  of  Coal 

Metric  tons 
(Metric  ton  = 
1.1023  short  tons) 

Clackmannan  and  Perth  

17 
38 
40 
6 

37 
25 
Few 
13 
7 
27 
8 
8 

2 

20  to  50  feet 
100  to  140  '  ' 
75 
I3l 

105 
59 
Small 
43 
i6J 
80 
40 
45 
Unknown  pos- 
sible reserve 
5 

41 
148 
130 
61 

128  i 
135 
58 
275 
73 
33° 

26J 
2 

3 

B2,B3 
B2,B3 
Blt  B2,  B3 

BJ,  BI 

B».  B3 
Alt  A2,  BI,  B2,  B3 
B2 
Alf  A2,  BI,  B2,  B3 
B2 
A.,  BI,  B2 
B2 
Bi.Bi 

BI 

916,243,044 
5,263,432,444 
4,252,000,000 
683,663,883 

3,143,148,115 
1,600,629,550 
324,187,635 
3,051,734,030 
134.965,370 
1,337,992,870 

1,000,000 

Under  the  Firth  of  Forth  

Edinburgh,  Haddington  and 
Peebles                

Stirlingshire  
Dumbartonshire  

Lanarkshire  
Renfrewshire  

Ayrshire  

Dumfriesshire  

Argyllshire  (Marvern)      .  .       .   . 

Sutherlandshire  

21,376,493,625 

1  For  description  of  classes  of  coal  see  under  Classification  of  Coals,  Chapter  V. 

In  addition  to  the  actual  tonnage  reserve  for  Scotland  mentioned 
in  the  above  table  there  are  probable  reserves  of  1,685,000,000  metric 
tons  in  seams  over  2  feet  thick  lying  between  4000  and  6000  feet  in 
depth  in  the  Firth  of  Forth,  and  in  the  Fife  and  Kinross  districts. 

The  coals  of  Great  Britain  are  all  of  the  higher  ranks,  bituminous, 
semibituminous  and  anthracite.  In  England  and  Wales  they  all 
occur  in  the  Coal  Measures  proper,  or  the  Pennsylvanian  as  the 
term  is  used  in  the  United  States.  In  Scotland  the  Lower  Carbon- 
iferous (Mississippian)  carries  good  coal  and  there  are  thin  workable 
seams  in  the  Calciferous  sandstone.  The  latter  is  a  formation  in 
the  lower  part  of  the  Lower  Carboniferous  and  should  not  be  con- 
fused with  part  of  the  Devonian  of  America. 


414       THE   COAL   FIELDS  OF   THE   WORLD— EUROPE  AND   ASIA 

In  England  and  Wales  the  Millstone  grit  is  well  developed  and  in 
some  places  it  is  very  thick,  reaching  about  5500  feet  in  thickness 
in  Lancashire.  As  in  America  it  consists  of  quartz  conglomerate 
and  micaceous,  arkosic  sandstone.  It  carries  small  seams  of  coal. 
In  Scotland^it  is  in  most  places  comparatively  thin  and  it  is  a  sand- 
stone known  as  "  Moor  rock.  "  This  rock  also  carries  thin  coal 
seams. 

The  Coal  Measures  reach  a  maximum  thickness  of  between  10,- 
ooo  and  12,000  feet  in  Wales  and  in  the  midst  of  the  series  there 
is  a  sandstone  and  conglomerate  known  as  the  Pennant  grit.  It 
is  in  many  places  almost  barren  of  coal  but  in  others  there  are  a 
number  of  good  seams.  In  a  few  localities  it  carries  pebbles  of  coal 
showing  that  vegetal  matter  had  already  formed  coal  which  could 
be  eroded  when  this  formation  was  laid  down.  In  many  of  the  coal 
fields,  fire  clay  or  "  seat  earth  "  is  found  beneath  the  coal  seams, 
leading  early  writers  to  consider  that  this  was  always  an  accom- 
paniment of  coal  seams.  Iron  ore,  in  form  of  the  carbonate,  often 
known  as  "black  band,  "  occurs  in  a  number  of  the  fields.  This 
ore  owes  its  origin  to  the  presence  of  abundant  carbon  dioxide  de- 
rived from  decaying  vegetation  in  the  waters  when  the  iron  was 
laid  down. 

Cannel  coal  is  abundant  in  some  fields,  and  some  of  it  carries 
numerous  fish  remains  showing  that  the  spores  which  formed  the 
coal  were  laid  down  in  ponds  of  open  water  where  fish  could  live. 
A  peculiar  coal  known  as  Torbanite,  which  is  a  boghead,  has  long 
been  mined  at  Torbane  Hill,  Scotland.  It  is  similar  to  an  oil  shale 
in  the  products  derived  from  distillation  but  it  is  nevertheless  a 
type  of  coal.  Its  status  was  once  fixed  by  law  in  an  important  suit. 

Some  fields  are  greatly  faulted  as,  for  example,  the  Cumberland 
field,  and  others  are  extensively  intruded  by  basalt  and  other  igneous 
rocks,  especially  some  of  the  Scottish  fields  and  the  Coalbrook- 
dale  and  Dudley  fields  of  England.  Mining  has  been  carried  on 
in  England  to  a  great  depth,  in  some  places  exceeding  3000  feet. 

South  Wales.1 -- This  famous  coal-field  occurs  in  parts  of  Mon- 
mouth,  Glamorgan,  Brecknock  and  Carmarthen  counties.  It  oc- 
cupies a  syncline  with  steeply  dipping  strata  on  the  southern  limb. 

1  Strahan,  A.,  and  Pollard,  W.,  Coals  of  South  Wales  with  special  reference  to  the 
origin  and  distribution  of  anthracite.  Memoir  Geol.  Survey,  England  and  Wales,  1915. 


SOUTH  WALES  415 

The  Coal  Measures,  which  reach  a  thickness  of  nearly  12,000  feet, 
may  be  divided  into  three  divisions:  a  lower  consisting  mainly  of 
shales  and  containing  the  bulk  of  the  coal  seams;  a  middle  series 
known  as  the  Pennant  series  consistly  chiefly  of  sandstone  and  coal- 
bearing  only  in  the  western  part  of  the  field;  and  an  upper  series 
consisting  mainly  of  shales  carrying  coal  seams.  The  anthracite 
occurs  near  the  northwestern  and  western  part  of  the  field  and  the 
same  seams  occur  as  bituminous  coal  in  the  southern  and  eastern 
portions  of  the  field  with  the  well-known  semibituminous,  smoke- 
less steam  coals  lying  between  the  two  extremes,  (Fig.  33).  In 
one  part  of  the  field  the  anthracite  reaches  an  undetermined  depth. 
There  is  one  condition  which  remains  almost  constant  throughout 
the  field  and  that  is  the  higher  fixed  carbon  of  the  coal  in  the  deeper 
seams.  In  any  section  there  is  in  almost  every  case  a  nearly  uni- 
form increase  in  the  fuel  ratio  with  depth.  This  has  not,  however, 
been  responsible  for  the  origin  of  the  anthracite.  Strahan  and  Pol- 
lard concluded  that  they  could  find  no  satisfactory  explanation  for 
the  occurrence  of  the  anthracite  in  one  part  of  the  field,  semibitu- 
minous in  another  part  and  bituminous  in  another,  as  there  are  no 
igneous  intrusions,  there  is  no  particular  difference  in  the  character 
of  the  vegetation  forming  the  coal  in  different  parts  of  the  field, 
and  the  depth  of  burial  or  the  length  of  time  since  burial  will  not 
account  for  the  changes.  They  also  doubt  that  pressure  could  cause 
the  difference,  but  the  writer  believes  that  this  is  the  only  satisfactory 
explanation.  The  relative  proportions  of  the  various  varieties  of 
coal  have  been  placed  as  bituminous  30.42  per  cent;  semibituminous, 
or  steam  coal,  47.31  per  cent;  anthracite  22.27  Per  cent. 

In  Glamorganshire  the  number  of  seams  varies  from  twelve  at  the 
eastern  end  with  an  aggregate  of  42  feet  of  coal  to  about  forty  in 
the  western  part  with  120  feet  of  coal.  In  Pembrokeshire  the  Pennant 
series  is  found  throughout  the  field.  The  number  of  seams  in  the 
eastern  part  runs  from  eight  with  21  feet  of  coal  to  eighteen  with  an 
aggregate  of  33  feet  in  the  western  part.  The  strata  are  highly  dis- 
turbed and  the  coal  is  all  anthracite. 

It  is  believed  that  there  is  a  large  deposit  of  coal  under  Swansea 
and  Carmarthen  bays.  A  large  fault  with  a  throw  of  approximately 
3000  feet  runs  under  Swansea  Bay  and  cuts  the  coal  field  so  as  to 
duplicate  the  measures. 


41 6       THE   COAL   FIELDS   OF  THE  WORLD— EUROPE   AND  ASIA 

Ireland.1  —  There  are  several  coal  fields  in  Ireland,  the  largest 
being  the  Leinster  field  covering  95  square  miles  in  Kilkenney,  Carlow 
and  Queen  counties.  The  coals  occur  in  the  Coal  Measures  and  the 
seams  which  are  worked  are  quite  thin,  varying  from  i  foot  8  inches, 
to  4  feet.  The  Ballycastle  field,  4!  square  miles  in  area,  in  County 
Antrim,  contains  seams  4  to  6  feet  thick  in  the  Lower  Carboniferous. 
Numerous  intrusions  of  dolerite  cut  this  field.  The  Tyrone  field 
carries  a  number  of  seams  in  the  Coal  Measures  running  up  to  9 
feet  in  thickness  and  the  Gortnaskea  seam  is  6  feet  thick  with  22 
inches  of  cannel.  Other  fields  are  the  Lough,  Allen  and  the  Tipper- 
ary,  besides  other  very  small  and  scattered  areas.  In  very  few 
places  in  Ireland  have  the  Coal  Measures  been  covered  by  later 
rocks,  and  tremendous  areas  of  these  rocks  have  been  eroded  from 
the  island. 

France.2  —  France  is  deficient  in  coal  for  her  future  need  as  a 
great  manufacturing  country,  and  during  the  Great  War  she  was 
cut  off  almost  entirely  from  her  best  coal  fields,  which  lie  in  the 
northeast.  The  coal  areas  have  been  divided  into  five  regions  by 
M.  Defline  as  follows:  (i)  North  of  Ardennes  Massif;  (2)  Eastern 
area;  (3)  In  Armorican  Massif;  (4)  In  Central  Massif;  (5)  In  Alps, 
Maures,  Pyrenees  and  Corsica. 

The  most  important  area  is  that  of  Valenciennes  where  the  quality 
of  the  coal  varies  from  anthracite  to  high  volatile  bituminous.  The 
beds  occur  in  the  Westphalian  series  of  the  Coal  Measures.  There 
are  a  large  number  of  seams,  in  the  north  basin  as  many  as  69,  but 
none  are  very  thick,  2  meters  being  near  the  maximum.  Parts  of 
the  Coal  Measures  have  been  faulted  beneath  the  Silurian  and  Dev- 
onian formations  and  in  the  Pas-de-Calais  basin  the  strata  are  ex- 
tensively faulted  and  folded,  (Fig.  73).  A  considerable  amount 
of  coal  lies  more  than  4000  feet  from  the  surface.  The  Boulonnais 
basin  which  is  a  continuation  of  that  of  Valenciennes  is  concealed 
by  Cretaceous  and  Jurassic  strata  and  the  coal  has  been  reached  by 
borings.  This  basin  is  very  small. 

1  Cole,  B.  A.  J.,  and  Lyburn,  E.  St.  John,  The  coal  resources  of  Ireland.     Coal  Re- 
sources of  the  World,  Vol.  II,  p.  629. 

2  Defline,  M.,  Les  ressources  de  la  France  en  combustibles  mineraux.'    Coal  Resources 
of  the  World,  Vol.  II,  p.  649.     Reports  on  individual  coal  fields  in  the  publications  of  the 
Department  of  Public  Works,  Paris  under  the  head  of  Etudes  des  Gttes  Mineraux  de  la 
France. 


FRANCE  417 

The  basins  in  the  east  include  Pont-a-Moussqn  and  Ronchamp. 
The  former  is  a  prolongation  of  the  Saarbruck  basin  and  the  Coal 
Measures  are  completely  concealed  beneath  Triassic  and  Permian 
rocks  at  a  depth  between  2000  and  3000  feet.  The  measures  belong 
to  the  Stephanian  and  Wesphalian  series  and,  judging  from  borings, 
there  are  from  one  to  seven  seams  with  a  maximum  aggregate  of 
about  20  feet  of  coal,  although  the  coal-bearing  strata  have  not 
been  penetrated.  Ronchamp  field  is  in  the  small  basin  overlain 
by  Permian  strata.  The  Coal  Measures  belong  to  the  Stephanian. 
There  are  3  to  6  meters  of  bituminous  coal  in  three  seams. 


FIG.  136.  —  Coal  mine  near  St.  Etienne,  France.     (Photo  by  E.  S.  Moore.) 

The  basins  in  the  Armorican  Massif  include  the  Cotentin,  Maine, 
Basse-Loire  and  Vendee.  In  the  first  field  the  coals  are  Stephan- 
ian and  are  of  little  importance  since  they  are  thin  and  of  poor 
quality.  The  Maine  field,  in  Brittany,  contains  coals  of  Dinantian 
or  Lower  Carboniferous  age.  The  coal  is  an  impure  anthracite  and 
occurs  in  very  irregular  seams,  one  reaching  60  meters  in  thickness 
at  one  point.  The  Basse-Loire  field  is  also  of  Dinantian  age  and  the 
rocks  are  highly  folded  and  faulted.  The  coal  is  of  poor  quality. 
The  Vendee  field  is  of  Westphalian  age  and  the  coal  beds  overlie 
gneiss  and  schist. 

In  the  Central  Massif  there  are  a  great  number  of  small  areas 


41 8       THE    COAL   FIELDS  OF   THE   WORLD— EUROPE   AND   ASIA 

of  which  the  St.  Etienne  basin,  near  the  town  of  that  name,  is  the 
most  important.  The  Coal  Measures  rest  on  granite  and  gneiss 
and  belong  to  the  Stephanian  series.  The  coal  contains  from 
7  to  35  per  cent  volatile  matter.  There  is  one  seam  known 
as  the  Grande  Couche  which  reaches  a  thickness  of  15  meters  in 
this  field  and  20  meters  in  the  Commentry  basin.  The  number 
of  seams  runs  as  high  as  thirty-five  in  the  St.  Etiehne  basin. 

The  other  fields  in  this  region  are  all  small,  and  the  rocks  are  of 
Stephanian  age.  The  Commentry  basin  is  one  of  the  most  inter- 
esting. It  is  9  by  3  kilometers  in  diameter,  and  is  characterized  by 
the  large  size  of  the  boulders  in  the  conglomerates  in  the  Coal  Meas- 
ures. Some  writers  have  suggested  that  these  may  be  of  glacial 
origin  and  others  that  they  may  be  due  to  torrential  streams  carry- 
ing the  material  into  a  lake.  It  was  in  this  basin  that  Fayol  found 
the  trees  with  tops  headed  downwards,  which  he  regarded  as  evi- 
dence of  drift  origin.  Some  of  the  conglomerate  in  the  Coal  Meas- 
ures carries  pebbles  of  coal  apparently  derived  from  previously  ex- 
isting coal  seams. 

In  the  Alps  seams  of  highly  folded  and  for  the  most  part  inferior 
anthracite  outcrop  at  various  points  from  Briancon  to  the  Little 
St.  Bernard  and  run  over  into  Italy  and  Switzerland.  The  seams 
are  irregular  in  extent  and  thickness  and  reach  a  maximum  thick- 
ness of  about  10  meters. 

Lignite  occurs  in  an  important  basin  known  as  the  Fuveau  basin, 
also  in  less  important  areas  in  the  Vosges  Mountains  and  in  the 
Rhone  basin.  The  Fuveau  deposits  are  of  Upper  Cretaceous  age 
and  the  seams  run  up  to  2  meters  in  thickness.  The  lignite  in  the 
Vosges  Mountains  is  Triassic  and  Jurassic  in  age  and  that  in  the 
Rhone  basin  is  Upper  Cretaceous  and  Tertiary. 

Spain  and  Portugal.1  --  The  most  important  coal-bearing  provinces 
of  Spain  are  Asturias  and  Leon  in  the  northwest  and  Teruel  in  the 
east.  In  age  the  coals  are  Upper  Carboniferous,  Cretaceous  and 
Tertiary,  and  they  vary  from  anthracite  to  lignite.  In  Asturias 
there  are  as  many  as  eighty  seams  with  112  feet  of  coal,  but  as  a  rule 
the  seams  are  not  numerous  and  none  of  them  are  very  thick.  The 
older  coals  are  anthracite  to  bituminous  and  the  Cretaceous  and 
Tertiary  coals  lignite  or  subbituminous. 

1  Coal  Resources  of  the  World. 


ITALY  419 

Portugal  has  little  coal.  Near  S.  Pedro  de  Cova  there  is  a  folded 
area  of  Coal  Measures  carrying  anthracite,  and  near  Tigueira  the 
upper  Jurassic  strata  contain  bituminous  coal  of  medium  quality. 

Switzerland.1 — This  is  an  old  mining  state  in  which  coal  has 
been  mined  for  over  two  and  a  half  centuries.  The  reserves  for  the 
future  are  not  over  80,000  metric  tons.  The  coal  is  Carboniferous, 
Jurassic,  Eocene  and  Pleistocene  in  age  and  on  account  of  the  ex- 
cessive folding  and  compression  which  the  rocks  have  suffered  most 
of  it  has  been  changed  to  anthracite  and  some  of  it  even  to  graphite. 


FIG.  137.  —  Highly  faulted  and  squeezed  coal  seam  in  the  mountains  of 
Switzerland. 


There  is  a  little  lignite  of  Eocene  and  Pleistocene  age.  The  reserves 
of  Switzerland  in  metric  tons  are  placed  at  4000  tons  actual  and 
50,000  tons  probable  reserve  in  anthracite,  and  500  tons  actual  and 
25,000  tons  probable  reserve  in  brown  coal,  or  a  total  of  79, 500  metric 
tons.  Much  of  this  coal  is  difficult  to  mine  owing  to  disturbances 
which  the  rocks  have  suffered. 

Italy.2  —  Italy  has  but  little  coal  and  all  but  about  i  per  cent 
of  the  coal  produced  is  lignite  or  subbituminous  in  rank.  Anthracite 
of  Carboniferous  age  occurs  in  many  places  in  highly  folded  rocks 
but  most  of  it  is  of  little  economic  importance.  Most  of  the  lignite 
and  subbituminous  coal  mined  comes  from  Tuscany  and  Umbria 
but  these  coals  are  widely  distributed  throughout  the  country.  Beds 
up  to  30  meters  in  thickness  are  reported  as  occurring  in  Tuscany. 
The  age  of  the  coal  is  Carboniferous,  Triassic,  Eocene,  Miocene  and 
Pliocene. 

1  Coal  Resources  of  the  World. 

2  Coal  Resources  of  the  World. 


420       THE  COAL   FIELDS  OF  THE   WORLD— EUROPE  AND  ASIA 


r 


Belgium.1  —  This  country  is  comparatively  well 
supplied  with  high-grade  coal.  The  seams  all 
occur  in  the  Coal  Measures  which  are  divided 
into  the  Upper  or  Stephanian  and  the  Lower  or 
Namurian  series,  the  former  carrying  the  bulk 
of  the  coal  in  the  Flenu  and  Charleroi  forma- 
tions. There  are  three  fields  in  Belgium:  (a) 
Dinant  field  in  the  southern  part  of  the  country 
and  including  numerous  isolated  small  basins 
within  a  large  syncline;  (b)  Namur  field  in  the 
central  part  of  the  Haine-Sambre-Meuse  trough; 
and  (c)  Campine  field  in  the  north.  The  Dinant 
fieldas  unimportant.  The  Campine  field  contains 
the  largest  estimated  reserves,  they  being  placed 
at  8,000,000,000  metric  tons.  This  field  has  not 
yet  been  worked  as  the  coal  lies  deep  and  our 
knowledge  is  confined  chiefly  to  borings.  The 
Namur  field  is  estimated  to  contain  3,000,000,000 
metric  tons  reserve,  and  while  there  are  numerous 
seams  they  seldom  exceed  2  meters  in  thickness. 
The  structure  of  the  basin  is  complex,  (Fig.  138). 
In  1910  the  average  thickness  of  the  seams  worked 
was  0.65  meters.  The  coal  is  chiefly  bituminous 
with  some  cannel.  Part  of  this  basin  is  very  deep 
and  the  deepest  coal  mines  in  the  world,  about 
3900  feet,  are  found  here.  About  one  half  of  the 
coals  of  Belgium  are  coking. 

Netherlands.  —  The  Coal  Measures  in  the 
Netherlands,  which  only  outcrop  in  the  south 
and  east,  are  of  the  same  age  as  those  of  Belgium 
and  those  of  Westphalia  between  which  they  form 
a  connecting  link.  The  strata  occur  as  great 
fault  blocks.  There  are  five  possible  fields  of 

1  Renier,  Armand,  Les  ressources  houill&res  de  la  Belgique. 
Coal  Resources  of  the  World.  Vol.  Ill,  p.  801.  Also,  Stanier, 
X.,  Des  rapports  entre  la  composition  des  charbons  et  leurs  con- 
ditions de  gisement.  Annales  Mines  Belgique,  V.  1900;  and 
Denoel,  L.,  carte  et  tableau  synoptique  des  sondages  du  bassin 
houiller  de  la  Campine.  Annales  Mines  Belgique,  IX,  1904. 


GERMANY  421 

which  two  are  comparatively  well  known:  (i)  South  Limburg  with  a 
maximum  aggregate  of  38  meters  of  coal  of  anthracite  and  bituminous 
rank;  (2)  South  Peel  of  which  little  is  definitely  known  but  which 
is  likely  to  be  a  comparatively  large  field.  The  other  fields  are 
known  only  by  a  few  test  borings.  The  coals  are  anthracite, 
semibituminous  and  bituminous  with  a  good  deal  of  gas  coal. 

Denmark.  —  Denmark  has  no  coal  production  although  before 
1880  lignite  was  mined  on  Bornholm  Island  from  Jura-Trias  forma- 
tions. There  are  nearly  fifty  seams  but  all  are  thin.  On  the  Faroes 
Islands  and  in  Iceland  coal  of  Tertiary  age,  which  has  been  changed 
locally  from  lignite  to  anthracite  by  basaltic  flows  and  intrusions, 
is  mined  for  local  use. 

Germany.1  —  Germany  contains  the  largest  supplies  of  coal  of 
any  of  the  European  countries  so  far  as  known.  The  coals  are  of 
Carboniferous,  Permian,  Cretaceous,  Tertiary  and  Pleistocene  ages. 
The  Tertiary  and  Pleistocene  coal  is  lignite,  or  Braunkohle,  and 
the  Carboniferous  is  bituminous  coal,  or  Steinkohle.  There  are  six 
districts  containing  Carboniferous  strata,  as  follows:  (i)  Saar;  (2) 
Westphalia  and  Rhine  province;  (3)  Lower  Silesia;  (4)  Upper  Silesia; 
(5)  Saxony;  and  (6)  Left  of  the  Rhine.  Saxony  contains  some  Permian 
beds.  There  are  considerable  areas  of  Cretaceous  coals  which  are 
but  little  known  and  there  are  four  districts  containing  lignite.  The 
latter  are:  (i)  Prussia  and  the  North  German  States;  (2)  Saxony  with 
Oligocene  and  Miocene  beds;  (3)  Bavaria;  and  (4)  Hesse,  the  latter 
two  containing  coals  in  undifferentiated  Tertiary  formations. 

The  Saar  district  includes  parts  of  Alsace-Lorraine,  Prussia  and 
the  Palatinate  in  which  a  large  area  of  the  Coal  Measures  (Ott- 
weiler  and  Saarbruck  formations)  together  with  Permian  and  Meso- 
zoic  formations  have  been  folded  into  a  large  anticline.  Erosion  has 
removed  the  upper  beds  so  that  the  Coal  Measures  are  well  exposed 
except  in  the  southwest  portion  where  they  are  deeply  buried  and 
much  water  in  porous  strata  causes  trouble  in  mining.  The  total 
thickness  of  coal  worked  amounts  to  over  40  meters  and  the  forma- 
tions are  divided  in  vertical  section  according  to  the  types  of  coals 
which  they  contain,  as  follows:  The  fat  coal,  the  lower  flaming  coal 
group,  the  upper  flaming  coal  group,  and  the  dry  coal  group.  The 

1  Die  Kohlenvorrate  des  Deutschen  Reiches.  Coal  Resources  of  the  World.  Vol. 
Ill,  p.  821. 


422       THE   COAL   FIELDS  OF  THE   WORLD— EUROPE  AND   ASIA 

rocks  have  been  extensively  faulted  and  intruded  by  igneous  rocks, 
(Fig.  139).     There  are  many  deep  mines  in  this  district. 

There  is  a  connection  between  the  coal-bearing  formations  along 
the  Rhine,  in  Westphalia,  Holland,  Belgium  and  France.  The  coals 
occur  in  the  Upper  and  Lower  Carboniferous.  In  Westphalia  and  on 
the  right  side  of  the  Rhine  the  beds  are  gently  folded  and  but  little 
faulted.  On  the  left  side  of  the  river  they  are  extensively  faulted. 

SECTION  THROUGH  THE  SAAR  COAL  BASIN 
(.AFTER  HEISE-HERBST) 


Neunkirchen  Lebach 


Lean  CoalB  Group          Upper  Lower          Fat  Coals  Group 


0  5  10  15Kio. 

FIG.  139.  —  Section  through  the  Saar  basin. 

The  Coal  Measures  are  buried  to  a  depth  of  700  meters  in  some 
places  by  Triassic,  Cretaceous  and  Tertiary  formations,  and  thick 
deposits  of  quicksand  in  the  latter  formations  have  made  special 
mining  methods  necessary.  On  the  left  side  of  the  Rhine  the  coal 
may  reach  a  maximum  aggregate  of  32  meters,  while  on  the  right 
side  the  maximum  thickness  is  about  30  meters  with  a  maximum 
of  thirty-three  seams. 

The  main  feature  in  the  Lower  Silesian  districts  is  the  depth  of 
the  basin,  which  exceeds  2000  meters  in  the  center,  and  the  Coal 
Measures  are  deeply  covered  by  Cretaceous  and  other  rocks.  The 
basin  is  extensively  faulted  and  crushed  and  igneous  intrusions  are 
abundant,  with  the  result  that  considerable  coal  has  been  coked 
by  natural  processes.  The  mines  are  very  gaseous.  The  coal  is 
chiefly  Upper  Carboniferous  but  to  some  extent  Lower  Carbonifer- 
ous in  age.  The  coal  is  described  as  being  platy  (probably  splint 
coal),  fibrous  and  dull,  and  some  of  it  is  cannel  coal. 

Upper  Silesia  is  a  very  important  field,  the  second  in  Germany  in 
importance.  It  is  noted  for  the  number  and  thickness  of  its  seams. 
They  are  not  so  deeply  buried  as  those  of  the  Lower  Silesian  dis- 


AUSTRIA  423 

trict,  not  being  over  150  meters  below  the  surface,  but  the  Carbon- 
iferous strata  are  very  thick.  They  reach  7000  meters  in  the  south- 
western part  of  the  district.  The  coals  are  Upper  Carboniferous 
in  age  and  the  strata  may  be  divided  into  a  lower  marine  group 
(Randgruppe)  and  an  upper  brackish  group  (Muldengruppe) .  It 
is  near  the  base  of  the  latter  that  the  thick  coal  seams  occur.  In 
the  western  part  of  the  district  there  are  said  to  be  477  seams  con- 
taining an  aggregate  of  272  meters  of  coal,  124  of  these  seams  being 
workable  and  carrying  172  meters  of  coal.  In  the  eastern  part  are 
105  seams  of  which  30  are  workable,  and  they  contain  62  meters  of 
coal.  The  Upper  Silesian  field  extends  into  what  were  formerly 
parts  of  Russia  and  Austria.  It  is  highly  folded  but  little  faulted. 

Coal  mining  has  been  carried  on  in  Saxony  since  the  tenth  century 
and  the  better  seams  are  practically  exhausted  in  the  Lower  Car- 
boniferous strata.  The  coal  is  now  procured  on  a  small  scale  from 
the  Upper  Carboniferous  and  Permian  formations. 

Lignite  occurs  extensively  in  Prussia  and  the  North  German  States, 
especially  in  the  Saxony-Thuringia  district.  The  beds  range  from 
Eocene  to  Miocene  in  age.  These  lignites  have  been  extensively 
employed  for  briquetting  and  for  the  production  of  by-products,  such 
as  gas,  oils  and  paraffin. 

Brown  coals  running  from  Miocene  to  Pleistocene  in  age  occur  in 
parts  of  Bavaria,  and  a  small  deposit  of  Oligocene  age  in  this  prov- 
ince is  believed  to  be  of  undoubted  drift  origin. 

Austria.1  —  There  are  three  main  coal-bearing  areas  in  Austria. 
These  are  in  the  Alps,  at  the  foot  of  the  Alps,  and  in  northern  Austria. 
In  the  Alps  there  are  coals  of  Carboniferous,  Triassic,  Jurassic, 
Upper  Cretaceous  and  Miocene  age.  The  Miocene  coals  are  lig- 
nites, the  seams  reaching  a  maximum  of  12  meters  in  thickness. 
The  others  are  bituminous  and  occur  for  the  most  part  in  thin  seams 
although  mined  in  many  places.  Along  the  foot  of  the  Alps  impor- 
tant reserves  of  lignite  occur  in  the  Miocene  rocks. 

In  parts  of  what  was  formerly  northern  Austria  extensive  depos- 
its of  lignite  of  Oligocene  and  Miocene  age  and  also  considerable 
beds  of  Upper  Carboniferous  coal  are  found  in  the  middle  Bohemian 

1  Petrascheck,  W.,  Die  Kohlenvorrate  Osterreichs.  Coal  Resources  of  the  World, 
Vol.  Ill,  p.  1013. 


424       THE   COAL   FIELDS   OF   THE  WORLD— EUROPE   AND   ASIA 

fields.  Thick  and  numerous  coal  seams  occur  near  the  Prussian 
boundary  but  they  are  covered  deeply  in  most  areas  by  later  rocks. 

Hungary.1  —  Hungary,  so  far  as  known,  is  deficient  in  coal  depos- 
its. She  has  lignite,  subbituminous  and  bituminous  coal.  The  lig- 
nite and  subbituminous  coals  occur  in  the  Jurassic,  Cretaceous,  Ter- 
tiary and  Quaternary  formations  and  the  bituminous  coals  in  the 
Carboniferous  and  Jurassic.  The  brown  coals  or  lignites  are  the 
only  really  important  coals  commercially.  A  considerable  amount 
of  the  lignite  formerly  belonging  to  Hungary  is  in  Croatia  and  Slav- 
onia. 

Bosnia  and  Herzegovina.2  —  The  deposits  of  these  states,  like  those 
of  many  other  countries  in  southern  Europe,  have  not  been  fully 
developed.  Coals  occur  in  Carboniferous,  Permian,  Triassic,  Creta- 
ceous and  Tertiary  formations,  but  the  principal  resources  of  these 
provinces  are  in  the  lignites  of  Tertiary  age  in  the  Zenica-Sarajevo, 
the  Ugljevik-Priboj  and  the  Baujaluka  areas  in  the  vicinity  of  Sa- 
rajevo, in  Bosnia.  In  the  Tuzla  basin  northeast  of  Sarajevo  there 
are  important  Pliocene  lignites  with  seams  reaching  10  to  20  meters 
in  thickness. 

Serbia.3  —  Like  the  last-named  states,  Serbia  has  coal  ranging 
from  Carboniferous  to  Tertiary  in  age.  The  upper  part  of  the  Coal 
Measures  lies  on  crystalline  rocks  and  carries  a  few  seams  of  mine- 
able coal  which  in  many  places  is  impure  and  requires  picking  and 
washing.  The  Upper  Cretaceous  carries  good  seams  of  coal  and 
also  rests  on  crystalline  rocks.  The  Jurassic  coals  are  dirty  but 
otherwise  of  fair  quality.  The  Cretaceous  and  Tertiary  coals  are 
lignites.  The  mineral  deposits  of  Serbia  are  as  yet  poorly  devel- 
oped. 

Roumania.4  —  The  most  important  coal  deposits  of  Roumania  are 
the  Pliocene  lignites  and  subbituminous  coals  of  the  Comanesti 
basin.  A  little  anthracite  is  mined  in  the  Carboniferous  of  the  Carpa- 

1  De  Papp,  Charles,  Les  Ressources  Houilleres  de  la  Hongrie.     Coal  Resources  of  the 
World,  Vol.  Ill,  p.  961. 

2  Katzer,  F.,  Die  Kohlenvorrate  Bosniens  und  der  Hercegovina.      Coal  Resources 
of  the  World,  Vol.  Ill,  p.  1075. 

3  Milojkovitch,  F.  A.,  Die  Kohlenvorkommen  Serbiens.     Coal  Resources  of  the  World, 
Vol.  Ill,  p.  1093. 

4  Marzec,  L.,  and  Tanaseseu,  I.,  Les  Reserves  de  Charbon  de  la  Rumanie.     Coal 
Resources  of  the  World,  Vol.  Ill,  p.  1107. 


TURKEY  425 

thians.  There  is  also  some  Mesozoic  coal.  The  anthracite  coal  is 
of  little  importance.  Roumania  has  apparently  not  developed  her 
coals  to  any  great  extent  and  very  little  seems  to  be  actually  known 
regarding  her  real  reserves. 

Montenegro.  —  This  state  carries  some  good  bituminous  coal  of 
Carboniferous  age,  one  seam  on  the  Albanian  frontier  reaching  over 
6  feet  in  thickness.  Little  attempt  has  been  made  to  develop  min- 
ing operations. 

Greece.  —  Coal  is  mined  in  Greece  only  at  Coumi,  but  lignite 
deposits  of  Tertiary  age  are  widely  distributed.  The  actual  reserve 
is  placed  at  10,000,000  metric  tons  and  the  probable  reserve  at  three 
times  this  figure.  With  the  redistribution  of  lands  in  Europe,  Greece 
will  receive  from  Turkey  in  Europe  the  principal  coal  field  of  that 
country,  lying  near  Keshan.  This  coal  is  of  bituminous  rank  and 
some  of  it  resembles  a  hard  cannel.  There  is  also  considerable  Ter- 
tiary lignite  on  the  Marmora  coast  and  at  Telvino  and  Triano. 

Bulgaria.1  —  Bulgaria  has  extensive  seams  of  coal  although  they 
have  not  been  developed  and  little  attempt  has  been  made  to  estimate 
her  reserves.  The  coals  are  of  three  varieties,  anthracite,  bituminous 
coal  and  lignite.  The  anthracite  lies  in  the  Isker  valley  and  while  it 
is  comparatively  dirty  and  the  seams  are  thin  the  volatile  constitu- 
ents are  less  than  4  per  cent.  It  is  Carboniferous  in  age.  Bitumi- 
nous coal  of  Cretaceous  age-is  found  in  much-folded  rocks  in  the  Balkan 
basin.  This  coal  is  used  in  making  briquets  and  in  coking.  It  is 
very  gassy.  The  seams  are  comparatively  thin. 

The  Tertiary  lignites  and  subbituminous  coals  are  widely  dis- 
tributed and  there  are  six  main  fields.  In  some  places  seams  range 
up  to  12  feet  in  thickness. 

Turkey.2  —  Turkey  has  retained  practically  no  coal  lands  in  Eur- 
ope. In  Asia  Minor  there  are  a  number  of  important  fields  of  Car- 
boniferous and  Tertiary  age.  Along  the  Aegean  and  the  Sea  of 
Marmora  there  are  good  Miocene  and  Pliocene  lignites  which  are 
mined  locally.  On  the  Asiatic  coast  of  the  Black  Sea  there 
are  bituminous  coals  in  the  Lower  Carboniferous,  or  Culm, 
and  in  the  Westphalian  and  Stephanian  series  of  the  Coal  Meas- 
ures. The  seams  are  numerous  although  not  thick,  and  mining  has 

1  Bontchew,  G.,  Coal  Resources  of  the  World,  Vol.  I. 

2  Dominian,  Leon,  Coal  Resources  of  the  World,  Vol.  I. 


426       THE   COAL   FIELDS  OF  THE   WORLD— EUROPE  AND  ASIA 

been  carried  on  at  a  number  of  places.  Some  areas  have  been  greatly 
faulted.  There  is  considerable  coal,  some  of  it  anthracite,  in  the 
eastern  part  of  Asia  Minor,  in  the  provinces  of  Bitlis  and  Erzoom. 
In  the  latter  province  lignite  is  mined.  Lignite  is  also  mined  in 
Syria,  near  Beirut.  Coal  has  been  mined  to  a  small  extent  in  Meso- 
potamia. 

Poland.  —  The  Dombrova  basin  contains  many  thick  seams,  es- 
pecially those  in  the  Reden  group  of  rocks  where  one  seam  reaches 
12  meters  in  thickness.  The  rocks  are  Carboniferous  in  age,  (Penn- 
sylvanian)  and  the  system  is  thick.  Much  faulting  has  occurred. 
The  upper  seams  contain  much  ash  and  in  many  places  the  coal 
is  mined  in  open  pits  as  the  measures  lie  near  the  surface  in  parts 
of  the  basin.  The  coal  of  Paleozoic  age  is  bituminous,  but  the 
northern  part  of  the  basin  contains  extensive  lignite  deposits  which 
are  also  mined.  Other  smaller  basins  which  are  not  well  known 
occur  in  this  country,. as  well  as  in  a  small  corner  of  the  Upper  Silesian 
field  which  lies  mostly  in  Germany. 

Russia.1  —  As  indicated  in  the  table  showing  the  resources  of  Eur- 
ope our  information  regarding  the  coal  fields  of  Russia  is  rather  in- 
definite since  very  little  knowledge  has  been  gained  concerning  the 
actual  reserves.  There  are  apparently  very  large  resources  in  an- 
thracite. The  best-known  basin  is  the  Donetz  which  has  furnished 
most  of  the  coal  mined.  This  is  the  most  important  Russian  area 
and  there  are  about  135  workable  seams  in  the  Lower  and  Upper 
Carboniferous  strata  in  this  field.  This  basin  is  so  folded  and  faulted 
as  to  make  mining  conditions  difficult  in  many  areas.  The  fuel  is 
bituminous  coal  and  anthracite,  the  latter  forming  about  13  per  cent 
of  the  output  (Plate  XVII.) 

The  Lower  Carboniferous  rocks  form  a  great  arc  where  they  out- 
crop and  approach  the  surface  in  the  Moscow  district.  The  main 
seams  occur  in  the  central  part  of  the  basin  and  they  are  known 
chiefly  from  borings  because  they  are  deeply  buried  by  Carboniferous 
limestones.  The  coal  is  chiefly  bituminous  but  some  boghead,  or 
cannel  coal  occurs. 

Considerable  bituminous  coal  mining  is  carried  on  along  the  west 
slope  of  the  Ural  Mountains  in  folded  Lower  Carboniferous  rocks. 

1  Tschernyschew,  Th.,  and  others,  The  coal  fields  of  Russia.  Coal  Resources  of  the 
World,  Vol.  Ill,  p.  1149. 


COAL  AREAS  OF  RUSSIA 


^•Paleozoic  ]        jMesozoic   Fi^ Tertiary 
••  ^  ^3 


SO         Longitude        35 


East     40 


0  50  100   200    300    400 

L-  —i- 

from  45        Greenwich        50 


PLATE  XVH.  —  The  coal  fields  of  European  Russia. 


(427) 


428       THE   COAL  FIELDS  OF  THE  WORLD— EUROPE   AND  ASIA 

Similar  conditions  exist  in  Siberia  along  the  east  slope  where  in  ad- 
dition to  bituminous  coal  there  is  a  great  deal  of  lignite  mined  in  the 
Mesozoic  and  Tertiary  formations  and  some  anthracite  is  dug  from 
closely  folded  basins  in  Carboniferous  rocks. 

The  Caucasus  district  contains  coal  of  Jurassic  and  Miocene  age, 
the  former  bituminous  coking  coal  and  the  latter  lignite.  The  Tur- 
kestan coals  are  of  little  importance  so  far  as  known  but  they  are 
in  age  Carboniferous,  Rhaetic  and  Jurassic.  The  coals  vary  from 
coking  bituminous  to  anthracite. 

Among  the  other  districts,  those  of  Sudjensk  and  Kuznetzk  give 
promise  of  being  important  as  there  is  over  100  feet  of  coal  in  about 
seventeen  seams.  The  coal  varies  from  high- volatile  gas  coal  to  semi- 
anthracite  and  is  Carboniferous  in  age.  Numerous  undeveloped 
areas  of  Permian  coal-bearing  rocks  are  known  to  occur  along  the 
Yenisei  River  but  they  have  not  been  extensively  prospected.  The 
coals  are  bituminous  in  character. 

Considerable  amounts  of  coal  of  Jurassic  and  Tertiary  ages,  vary- 
ing from  bituminous  coking  coal  to  lignite,  occur  in  the  Irkutsk 
and  other  basins.  The  Russian  Sakhalien  carries  coals  of  Upper 
Cretaceous  to  Pleistocene  age  and  of  bituminous  to  lignite  in  char- 
acter. Finland  is  without  commercial  coal  deposits  although  small 
quantities  of  anthracite  have  been  found.  Tertiary  lignites  are 
widely  distributed  over  European  and  Asiatic  Russia. 

Sweden,  Norway  and  Spitzbergen.1  —  Sweden  has  only  a  small 
coal  field,  in  the  province  of  Skane,  in  the  south.  The  fuel  is  high- 
volatile  bituminous  to  subbituminous  coal  and  it  occurs  in  Jura- 
Trias  formations  (Rhaetic-Liassic)  associated  with  fire  clays.  The 
seams  vary  from  6  inches  to  3  feet  in  thickness.  The  coal  is  mined 
at  a  number  of  places  and  the  estimated  reserves  amount  to  about 
115,000,000  tons.  Sweden's  production  of  coal  supplies  less  than 
8  per  cent  of  her  requirements  and  the  remainder  of  her  supply  is 
imported. 

Norway  has  no  coal  except  a  little  on  some  of  the  northern  islands. 
On  Ando  Island  a  seam  of  high-ash  cannel  coal,  i  meter  thick  occurs 
in  Jurassic  rocks.  It  has  not  been  mined.  Buren  Island  contains 
coal  of  Devonian  age  not  yet  worked.  This  is  probably  the  oldest 
known  coal  in  the  world. 

1  Coal  Resources  of  the  World. 


^y>  v  i  •/     •• 

.  I   O       /   *^  *\    ^ ' 

Hfll          .Ct  V 


COAL  AREAS  OF  ASIA 

Tertiary  Coals 
Mesozoic  Coals 
Paleozoic  Coals 


Longitude      80      East 


PLATE  XVm.— 


from     90        Greenwich 


Coal  fields  of  Asia. 


titiL 


ASIA  429 

Spitzbergen  has  been  known  for  many  years  to  contain  consider- 
able deposits  of  good  coal,  and  mining  operations  have  been  carried 
on  for  a  number  of  years  by  several  small  companies  and  by  one  large 
American  concern.  The  island  is  almost  covered  with  snow  and  ice 
most  of  the  year,  but  sufficient  information  has  been  collected  to 
fix  the  age  of  the  coal  deposits  as  Carboniferous,  Jurassic  and  Ter- 
tiary. The  only  valuable  Carboniferous  coal  so  far  located  is  at 
the  head  of  Ice  Fiord,  where  a  seam  7  meters  in  thickness  occurs. 
The  Jurassic  coals  so  far  as  known  are  unimportant.  The  Tertiary 
coal  occurs  near  the  base  of  the  Miocene  and  is  a  good  quality  of 
subbituminous  to  bituminous  coal.  It  is  mined  on  Advent  Bay 
by  an  American  company.  All  shipping  must  be  done  during  about 
three  summer  months  owing  to  the  unfavorable  weather  conditions. 
The  ground  is  said  to  be  frozen  to  a  maximum  depth  of  about  400 
meters  but  the  Tertiary  rocks  in  this  area  are  thick  and  the  mining 
operations  are  carried  on  without  great  hardship  in  spite  of  about 
four  months  of  continual  darkness.  On  account  of  the  scarcity  of 
coal  for  domestic  and  industrial  purposes  in  that  part  of  the  world 
the  Spitzbergen  output  finds  a  ready  market. 

Asia 

Asia  is  well  supplied  with  coal  although  little  is  yet  known  re- 
garding very  large  areas  of  that  continent.  The  following  table 
indicates  the  resources  of  the  continent  by  countries  and  provinces 
in  the  various  kinds  of  coal,  and  the  accompanying  map  of  the  con- 
tinent shows  the  distribution  of  the  coals,  (Plate  XVIII.) 

This  table  brings  out  two  important  points.  One  is  the  enormous 
resources  of  China  in  anthracite,  although  it  seems  probable  that 
considerable  coal  classed  as  anthracite  may  be  nearer  semianthracite 
and  semibituminous  coal  than  true  anthracite.  In  any  case  China 
leads  the  world  by  a  tremendous  margin  in  -this  commodity.  The 
other  point  is  the  lack  of  definite  knowledge  regarding  the  continent's 
coal  deposits.  A  few  of  the  other  countries,  especially  Siberia,  un- 
doubtedly have  large  reserves  which  are  little  known. 


430       THE   COAL   FIELDS  OF  THE  WORLD— EUROPE  AND  ASIA 
'COAL  RESOURCES  OF  ASIA   (IN  MILLIONS  OF  METRIC  TONS) 


Actual  Reserve 
(i  metric  ton  =  1.1023  short  tons) 

Probable  Reserve 

Total 

Class  of  Coal 

Class  of  Coal 

A 

BandC 

D 

A 

BandC 

D 

Subbitu- 

Anthracite 
and  semi- 
anthracite 

Bitumi- 
nous coals 

minous 
coals    and 
lignites 

Corea  

7 

I 

5 

33 

B              4 

22 

C             9 

81 

China: 

Chili  

6785 

B  6201 

3.242 

B      5,490 

C    292 

C         658 

Shantung.  . 

1360 

B  2842 

640 

B      2,241 

Shansi  

240 

B    123 

299,760 

B  414,217 

Shensi  

1,050 

Kansu  

B      5,129 

Honan  

6,575 

B      2,700 

Kiangsu.  .  . 

10 

Anhui  

B         187 

Hupei  

B         117 

Chekiang.  . 

18 

B            6 

Chekiang.  . 

120* 

Kiangsi  

B    325 

B      3,070 

Fukien  .... 

80* 

Kuangtung 

498 

256 

B         255 

Kuangsi  .  .  . 
Hunan.  .  .  . 

48,000 

500 
B    42,000 

Szechuan.  . 

20,000 

B    60,000 

500 

Kueichou  .  . 

B    30,000 

Yunnan.  .  . 

B    30,000 

100 

8883 

9783 

378,58i 

597,740 

600 

995,587 

Japan: 
Mesozoic 

coals    . 

4 

37 

B             5 

Tertiary.  .  . 

C            5 

Karaf  uto  . 

C      17 

C      i,345 

Hokkaido 

C    336 

C      2,106 

233 

Honsu  

i 

C        i 

67 

20 

C           14 

478 

Kyushu  .  . 

C    542 

C      2,374 

Taiwan.  .  . 

C         385 

5 

C    896 

67 

57 

6,234 

711 

7970 

Estimated  by  Kinosuke  Inouye. 


CHINA 

RESOURCES   OF  ASIA    (Continued) 


431 


•    • 

Actual  Reserve 
(i  metric  ton  =  1.1023  short  tons) 

Probable    Reserve 

Total 

Class  of  Coal 

Class  of  Coal 

A 

Anthracite 
and  semi- 
anthracite 

B  and  C 

Bitumi- 
nous coals 

D 

Subbitu- 
minous 
coals  and 
lignites 

A 

B  and  C 

D 

Manchuria.  . 
Siberia.  . 

B      31 
C    378 

B      48 

B      24. 
C      30 

C    119 

222 
3 

68 

i 

20,002 

B       223 
C       508 
B  66,034 

B  53,037 

C          210 

B  22,657 
B       246 

C         28 

107,844 

2,327 
50 

1,208 
173,879 

20,002 

Indo-China  . 
India: 
Bengal, 
Bikai  and 
Orissa  

Central 
India  

Central 
Provinces 

Mesozoic 
and 
Tertiary  .  .  . 

Persia  

221 

225 

76,178 
B     1,858 

2,377 

79,001 
1,858 

Total  in 
Asia  

8895 

11,310 

297 

398,742 

748,788 

111,554 

1,279,586 

1  From  Coal  Resources  of  the  World,  Vol.  I.  Estimate  based  on  all  seams  less  than  4000  feet  deep  and 
more  than  14  inches  thick,  together  with  all  seams  between  4000  and  6000  feet  deep  and  more  than  2  feet 
thick,  of  workable  coal.  For  description  of  classes  see  Classification  of  Coals,  Chapter  V. 

China.1  —  The  coal  deposits  of  China  are  widespread.  A  very 
large  area  occurs  in  northern  China  covering  most  of  the  southern 
part  of  the  province  of  Shansi,  and  another  large  field  is  found  in  the 
south  covering  parts  of  Hunan,  Kueichou,  Yunnan  and  Szechuan 
provinces.  The  age  of  the  coals  is  Permo-Carboniferous,  Rhaetic 
(Triassic),  Jurassic  and  Tertiary,  and  the  coals  vary  from  lignite  to 
anthracite.  Some  of  the  lignite  is  considered  as  Pliocene  in  age. 
The  anthracite  and  other  low- volatile  coals  occur  in  areas  which  are 

1  Drake,  N.  F.,  and  Kinosuke  Inouye,  The  coal  resources  of  China.  Coal  Resources 
of  the  World,  Vol.  I,  pp.  129-214. 


432        THE   COAL   FIELDS  OF  THE  WORLD— EUROPE   AND  ASIA 

more  folded  or  compressed  than  the  others,  and  considerable  areas 
have  been  so  crushed  as  to  be  almost  unmineable.  It  is  stated  that 
in  the  Sieu  River  district  in  Hunan  province,  where  much  anthracite 
is  mined,  the  seams  of  anthracite  average  15  feet  in  thickness,  and 
one  seam,  apparently  of  anthracite,  is  50  feet  thick.  There  is  a 
large  amount  of  good  coking  coal  in  the  country. 

Korea.1  —  Coal  has  been  mined  in  Korea  for  many  years  but  on  a 
small  scale  and  in  a  primitive  way.  The  coals  are  of  Paleozoic  (appar- 
ently Carboniferous),  Jurassic  and  Tertiary  age.  The  Carbonifer- 
ous coals  so  far  discovered  are  of  little  importance  but  little  is  known 
about  the  possibilities  of  the  rocks  of  this  age.  The  Jurassic  coals  are 
most  important.  The  Tertiary  coals  are  lignites.  Most  of  the  coal 
mined  is  semianthracite.  It  is  powdery,  and  is  sent  to  Japan  where 
it  is  made  into  briquets.  Japan  takes  nearly  all  the  production 
and  most  of  the  coal  used  in  Korea  is  imported. 

Manchuria.2  —  Manchuria  has  large  resources  in  coal  and  there 
are  a  large  number  of  small  mines  operated  in  a  primitive  way.  Large 
operations  are,  however,  being  carried  on  in  the  important  Fu-Shun 
field.  The  age  of  the  coal  is  Carboniferous,  Jurassic  and  Tertiary. 
The  coals  range  from  low  grade  bituminous  to  semianthracite.  Most 
of  the  coal  mined  is  from  the  Tertiary  and  it  varies  from  subbitu- 
minous  to  bituminous.  In  this  field  one  of  the  seams  has  a  remark- 
able thickness  and  mining  has  been  carried  on  for  many  centuries. 
It  is  stated  that  coal  was  mined  here  for  a  porcelain  factory  600  or 
700  years  ago  and  that  it  was  also  used  for  copper  smelting  possibly 
as  far  back  as  3000  years  ago.  Mining  was  prohibited  by  the  govern- 
ment in  the  eighteenth  century.  The  main  seam  in  the  Chien- 
chin-chai  section  varies  in  thickness  from  130  to  200  feet  with  nearly 
a  hundred  thin  partings  aggregating  about  20  feet.  The  quality 
of  the  seam  varies  considerably  where  folded,  shrinking  to  75  feet; 
and  the  partings  increase  to  an  aggregate  of  70  feet  in  130  feet  of 
coal.  The  coal  is  subbituminous  to  bituminous  and  is  low  in  sulphur 
and  ash. 

Japan.3  —  Mining  of  coal  has  been  carried  on  in  a  primitive  way 
in  Japan  for  centuries,  but  about  1868  real,  active  mining  began 

1  Kinosuke  Inouye,  Op.  cit.,  p.  215. 

2  Kinosuke  Inouye,  Op.  cit.,  p.  239. 

3  Kinosuke  Inouye,  Op.  cit.,  p.  279. 


INDIA  433 

under  foreign  engineers.  The  center  of  the  coal-mining  industry  is 
in  northern  KyQshu  and  large  mining  plants  are  also  in  operation  in 
Hokkaido.  Chikuho,  which  is  considered  the  richest  and  most  im- 
portant area,  is  well  developed,  and  the  Miike  field  is  developing 
rapidly.  Japan  exports  a  good  deal  of  coal  and  imports  little  al- 
though the  imports  from  China  are  growing. 

The  coals  of  Japan  are  Triassic  (Rhaetic),  Jurassic,  and  Tertiary 
in  age.  The  Rhaetic  and  Tertiary  are  of  most  importance,  the 
latter  being  the  best  of  all.  Most  of  the  Mesozoic  fields  are  small 
and  scattered  and  they  have  suffered  much  from  folding  and  igneous 
intrusions.  In  the  Tertiary  the  best  coals  occur  in  the  Miocene. 
There  is  some  lignite  in  the  Pliocene.  Some  semianthracite  coal 
occurs  in  the  Mesozoic  formations  and  natural  coke  occurs  near  ig- 
neous intrusions.  Most  of  the  coal  mined  is  bituminous,  much  of 
it  high-volatile.  There  is  considerable  coking  coal. 

The  Ishikan  coal  fields  are  remarkable  for  the  number  of  seams 
and  their  thickness.  In  the  lower  series  of  the  Tertiary  there  are 
said  to  be  as  many  as  150  seams,  lens-shaped,  and  ranging  from  a 
few  inches  to  60  feet  in  thickness.  The  coal  is  bituminous. 

India.1  —  Very  little  definite  information  is  obtainable  regarding 
the  extent  of  the  coal  deposits  of  India.  They  occur  in  the  Gond- 
wana  system,  of  Permo-Carboniferous  age,  and  in  the  Tertiary, 
both  in  the  Eocene  and  Miocene.  There  are  unimportant  and  little- 
known  areas  in  the  Jurassic  and  Cretaceous.  The  older  coals 
occur  only  in  the  Damuda  series  of  the  Lower  Gondwana  system. 
The  Damuda  series  overlies  the  Talchir  series,  which  is  of  glacial 
origin.  The  conditions  in  India  strongly  resemble  those  of  South 
Africa  and  Australia  where  the  coal  deposits  of  the  Permo-Carbon- 
iferous group  are  indirectly  associated  with  glacial  deposits  and  there 
are  the  same  types  of  plants  in  the  Glossopteris  flora. 

The  main  Gondwana  fields  occur  in  the  following  provinces:  Ben- 
gal, Bihar  and  Orissa,  Central  India,  Central  Provinces  and  the 
Nizam's  Dominions,  the  most  important  being  those  of  Bengal, 
Bihar  and  Orissa.  Active  operations  are  carried  on  in  the  Ran- 
iganj,  Giridih  and  Jherria  fields.  The  coal  is  of  bituminous  quality, 

1  Hayden,  H.  H.,  The  coal  resources  of  India.  Coal  Resources  of  the  World,  Vol.  I, 
p.  353.  See  also  Memoirs  Geol.  Survey  of  India,  Vol.  XLI,  by  R.  R.  Simpson. 


434      THE   COAL   FIELDS  OF  THE  WORLD— EUROPE   AND  ASIA 

a  good  deal  of  it  being  of  inferior  grade.  The  seams  have  been  in 
many  places  intruded,  broken  and  altered  by  igneous  rocks. 

In  the  Umaria  field  of  Central  India  mining  is  regularly  carried 
on.  In  the  Central  Provinces  there  are  three  basins,  Sarguja  and 
Chattisgarh  on  the  northeast,  the  Satpura  and  Chindwara  basin 
on  the  northwest  and  the  Godavari  basin  extending  for  nearly  300 
miles  down  the  Godavari  and  its  tributaries.  The  possibility  of  the 
rocks  of  the  Sarguja  basin  connecting  with  the  Satpura  basin  and 
these  again  with  those  of  the  Godavari  beneath  the  Deccan  trap 
has  been  suggested.  This  would  give  tremendous  reserves  not  yet 
exploited  or  computed.  The  Mesozoic  and  Tertiary  coals  occur  in 
Assam,  and  there  is  a  group  of  collieries  near  Margherita  opera- 
ting on  seams  aggregating  80  feet  of  coal.  The  coal  is  friable  and 
high  in  sulphur.  In  Baluchistan  a  colliery  is  operated  at  Khost,  but 
the  seams  of  this  district  are  thin  and  limited.  Burma  so  far  as 
known  has  little  good  coal. 

With  regard  to  the  countries  adjacent  to  India,  it  is  reported  that 
Afghanistan  apparently  has  large  coal  deposits,  but  little  is  known 
regarding  them.  Thibet  has  no  coal  so  far  as  known. 

Persia.1  —  Coal  is  widely  distributed  over  Persia  and  is  mined 
by  primitive  methods  for  local  use,  in  a  great  number  of  places.  Very 
little  is  known  regarding  the  extent  or  quality  of  most  of  the  seams. 

BRITISH  NORTH  BORNEO2 

The  coal  in  this  island  is  lignite  and  low-grade  bituminous  coal,  and 
it  is  almost  all  of  Tertiary  age.  The  better  coal  is  Eocene  but  there  is 
some  in  the  Oligocene,  Miocene  and  Pleistocene  formations.  A  num- 
ber of  mines  are  worked  and  the  labor  is  chiefly  Chinese,  Malay 
and  Javanese.  At  Brooketon  in  the  State  of  Sarawak,  there  are 
five  seams  with  thicknesses  of  28,  26,  29,  5  and  2  feet  respectively. 
The  first  two  of  these  seams  are  worked.  The  beds  are  tilted  up 
to  80  degrees.  The  coal  is  very  low  in  ash,  one  analysis  showing  only 
1.58  per  cent,  and  sulphur  is  low.  Spontaneous  combustion  occurs 

1  Rabino,  H.  L.,  The  coal  resources  of  Persia.     Coal  Resources  of  the  World,  Vol. 

I,  P-  365- 

2  Evans,  J.  W.,  The  coal  resources  of  British  Territory  in  North  Borneo.     Coal  Re- 
sources of  the  World,  Vol.  I,  p.  89.     Also  see  Coal  Mining  in  Borneo  by  James  Roden. 
Trans.  Inst.  Min.  Eng.,  Vol.  28,  p.  240, 1904-05. 


THE  PHILIPPINE   ISLANDS  435 

under  favorable  conditions  and  there  is  a  large  amount  of  water  in 
the  mines.  This  field  apparently  extends  under  the  sea  to  the  north 
end  of  the  Island  of  Labaun.  Some  of  the  coal  contains  a  large 
amount  of  resin  which  the  natives  use  for  lighting  purposes.  The 
Silimpopon  coal  field  on  the  river  by  that  name  is  near  the  coast 
and  shipments  can  readily  be  made.  There  is  little  gas  in  the  mines 
and  open  lights  are  used. 

DUTCH  EAST  INDIES,  OR  NETHERLANDS  INDIA1 

A  large  amount  of  coal  is  distributed  through  these  islands.  It 
is  all  Tertiary  in  age,  Eocene  and  Pliocene.  The  coal  is  of  lignitic 
and  subbituminous  rank.  The  production  of  the  island  of  Sumatra 
amounts  to  about  half  a  million  tons  a  year  and  this  comes  chiefly 
from  the  Soegar  area  of  the  Ombilin  field  in  which  some  seams  reach 
a  thickness  of  over  30  feet.  The  other  field  on  the  Sepoetih  River 
is  not  of  much  importance.  Java  contains  some  coal  but  the  seams 
are  thin.  Borneo  has  a  much  larger  supply  with  more  and  thicker 
seams  than  the  other  islands.  The  probable  resources  of  all  the 
islands  are  probably  about  one  billion  tons. 

THE  PHILIPPINE  ISLANDS2 

The  important  deposits  of  the  Philippines  are  all  Tertiary,  chiefly 
Miocene  in  age,  and  these  coals  are  mostly  lignitic  and  subbituminous, 
with  a  little  coal  of  bituminous  rank.  The  total  known  area  under- 
lain with  coal  seams  amounts  to  about  53  square  miles  of  which 
less  than  7  square  miles  are  of  workable  quality.  There  is  a  much 
larger  unprospected  area  which  will  no  doubt  prove  to  contain  val- 
uable seams.  The  fields  occur  on  the  islands  of  Baton,  Cebu,  Min- 
danao, Masbate,  Mindoro  and  Luzon.  On  Luzon  Island  the  coal 
is  around  Sugud  Bay,  and  on  the  Island  of  Mindanao  it  is  on  Si- 
buguey  Bay  in  the  southwest  corner  of  the  island.  Of  these  fields 
those  on  Baton  and  Cebu  islands  are  regarded  as  most  important. 
On  the  former  island  there  are  estimated  to  be  about  26,000,000 
tons  of  subbituminous  coal  in  two  to  eight  seams,  3  to  12  feet  thick. 
The  western  part  of  the  field  is  highly  faulted  and  folded. 

On  the  island  of  Cebu  the  coals  lie  from  8  to  15  miles  from  the  sea. 

1  Douglas,  E.  A.,  Coal  Resources  of  the  World,  Vol.  I,  p.  95. 
*  Dalburg,  F.  A.,  Coal  Resources  of  the  World.    Vol.  I,  p.  107. 


436      THE   COAL  FIELDS   OF  THE  WORLD— EUROPE   AND   ASIA 

The  coal  is  subbituminous  and  it  occurs  in  a  series  of  faulted  and 
folded  Oligocene  and  Miocene  strata  over  2000  feet  thick.  Some 
of  the  seams  reach  a  thickness  of  15  feet.  The  coal  on  Mindanao 
and  Polillo  islands  is  classed  as  bituminous  by  Dalburg.  That  on 
Mindoro  Island  near  Bulalacao  is  lignite  and  the  seams,  six  in  num- 
ber, run  up  to  12  feet  in  thickness.  On  Sugud  Bay,  Island  of  Luzon, 
the  seams  of  subbituminous  coal  vary  from  10  to  27  feet  in  thickness. 
The  beds  are  considerably  folded  in  parts  of  the  field. 

The  Philippine  coals  are  used  chiefly  by  inhabitants  of  the  islands 
for  domestic  purposes  and  on  ships,  and  in  recent  years  several  mines 
have  been  operated  on  a  fairly  large  scale.  In  most  cases  these 
are  controlled  by  American  mining  men.  Scarcely  any  of  the  coal 
cokes  well.  The  total  resources  of  the  islands  are  placed  at:  bitu- 
minous coal,  4,959,200;  subbituminous  coal,  31,285,200;  and  lig- 
nite (black)  30,092,000  metric  tons.  Apparently  the  black  lignite 
mentioned  in  the  reports  would  be  largely  classed  as  subbituminous 
coal  in  this  country  according  to  our  present  custom. 


40° 


Longitude        20"        West 


PLATE    XIX. —  The  coal  fields   of   Africa.     (From  "Coal  Resources  of  the  World," 
published  by  the  i2th  International  Geological  Congress,  Toronto,  Canada.) 

(437) 


CHAPTER  XV 


THE   COAL   FIELDS   OF   THE   WORLD  —  AFRICA   AND 

OCEANIA 

Africa1 

The  Dark  Continent  is  so  large  and  there  is  so  much  of  it  which 
has  not  been  thoroughly  explored  that  anything  like  an  attempt  to 
accurately  describe  its  coal  deposits  is  impossible  at  this  time.  The 
accompanying  map  (Plate  XIX)  shows  the  distribution  of  the  coals 
so  far  as  known  and  the  following  table  gives  the  estimates  of  the  re- 
sources as  compiled  by  the  International  Geological  Congress  in  the 
year  1913. 

RESOURCES  OF  AFRICA 


Actual  Reserve 
(In  millions  of  metric  tons) 
''i  metric  ton    =    1.1023  short  tons) 

Probable  Reserve 
(In  millions  of  metric  tons) 

Class  of  Coal 

Class  of  Coal 

Total 

Class  A 

Anthracite 
and  some 
dry  coals. 

Classes 
B  and  C 

Bituminous 
coals 

Class  D 
Subbitumi- 
nous  coals. 
Brown  coals 
and  lignites 

A 

BandC 

D 

Belgian  Congo  
Southern  Nigeria  .  .  . 
Rhodesia  

2 

B      306 
C        37 

80 
74 

4700 
6000 

960 

B          90 

B       119 

C          31 

B  28,800 
C    7,200 
B   4,600 

B    2,880 
C       960 

900 

990 

80 

569 
56,200 

South  Africa: 
Transvaal  

Natal 

Zululand  
Orange  Free  State.. 
Cape,  Basuto  and 
Swaziland 

1,  660 

44,440 

Total  

2 

343 

154 

1,  660 

44,680 

oo 

57,839 

For  detailed  description  of  classes  see  Classification  of  Coals,  Chapter  V.  The  reserves  are 
figured  on  all  seams  which  are  i  foot  or  over  in  thickness  and  less  than  4000  feet  deep;  and  on  all 
seams  of  2  feet  and  over  which  lie  between  4000  and  6000  feet  jn  depth. 

1  For  detailed  descriptions  of  deposits  in  Africa  see  Coal  Resources  of  the  World, 
Vol.  II,  pp.  375-428.  Also  Colonial  Reports  of  the  Museum  of  the  Imperial  Institute, 
London;  Reports  of  the  Department  of  Mines,  Union  of  South  Africa. 

438 


SOUTHERN  NIGERIA 


439 


The  geological  ages  of  the  coals  of  Africa  are  indicated  in  the  table 
given  below: 

GEOLOGICAL  AGES  OF  AFRICAN   COAL  DEPOSITS 


S 

?r 

* 

£H 

3 

o 

rt 

r  -3 

S 

q 

3 

'ca 

o 

i 

i 

1 

CO 

Abyssin 

a1 

11 

^Z 
eg 

1 

* 

a 

.% 

H 

Rhodesi 

3 

s 

H 

o  8, 

la 

I 

Pleistocene         

L 

Tertiary       

1  b 

1 

1 

L 

Upper  Cretaceous 

g 

Triassic   including  Rhaetic  . 

R  s 

bs 

Permian                  

p 

B 

Permo-Carboniferous 

b 

P 

a 

B 

1 

A,  Anthracite;  S,  Semibituminous;  B,  Bituminous;  B,  Subbituminous;  L,  Lignite;  C,  Cannel. 
Capital  letter  indicates  important  deposits,  lower  case  unimportant  or  unworkable  deposits. 

The  main  coal  fields  of  Africa  are  in  the  southern  portions  of  the 
continent.  Egypt  has  traces  of  lignite  and  bituminous  coal  but 
nothing  workable.  The  Anglo-Egyptian  Sudan  is  also  lacking  in 
workable  coal  although  traces  of  lignite  have  been  found.  Abys- 
sinia is  little  better  off,  but  according  to  Dum  and  Grabham  the 
natives  mine  coal  near  Addis  Abbaba,  the  capital  of  Abyssinia.  The 
East  Africa  Protectorate  has  no  workable  seams  and  Madagascar 
has  a  very  limited  amount  so  far  as  is  at  present  known.  In  the 
lanapera  area  of  the  island  there  are  several  seams  reaching  a  maxi- 
mum thickness  of  8  feet  4  inches,  and  according  to  Bonnefond  the 
coal  is  like  cannel  in  character. 

Southern  Nigeria.  —  In  southern  Nigeria  good  subbituminous  coal 
and  lignite  have  been  discovered.  The  former  is  probably  of  Creta- 
ceous and  the  latter  of  Tertiary  age.  According  to  J.  W.  Evans, 
the  best-known  lignite  areas  occur  in  the  vicinity  of  Onitsha  and 
Asaba  on  the  other  side  of  the  Niger  River.  In  the  latter  locality 
six  seams  of  lignite  ranging  from  8  to  20  feet  in  thickness  have  been 
examined,  and  this  coal  was  found  to  make  good  briquets  when 
tested  in  Europe  and  compared  with  the  German  lignites.  The 


440      THE   COAL   FIELDS   OF   THE   WORLD— AFRICA  AND    OCEANIA 

seams  of  subbituminous  coal  reach  nearly  6  feet  in  thickness  and 
they  outcrop  in  the  escarpment  about  45  miles  east  of  the  Niger 
River. 

Nyassaland  has  very  little  coal  which  is  sufficiently  clean  to  be 
utilized. 

Rhodesia.  —  The  Wankie  coal  field  is  the  only  one  in  Rhodesia 
where  coal  is  being  mined.  This  field  lies  about  60  miles  south- 
east of  Victoria  Falls  on  the  railroad  line  to  Bulawayo.  The  coal 
lies  in  the  basin  of  the  Zambesi  River  and  like  the  other  fields  of 
South  Africa  it  occurs  in  the  Karroo  series  which  apparently  in- 
cludes rocks  ranging  in  age  from  Carboniferous  to  lower  Jurassic, 
with  no  well-marked  lines  of  division  between  them.  The  main 
coal-bearing  formation  is  in  the  Lower  Matobola  which  corresponds 
to  the  Ecca  series  of  Cape  Colony  and  the  High  Veld  coal  measures 
of  the  Transvaal.  It  lies  just  above  the  Dwyka  conglomerate  which 
is  of  glacial  origin  and  usually  regarded  as  of  Permian  age.  Some 
geologists  have  considered  at  least  some  of  the  coal  beds  as  of  the 
same  age  as  the  Rhaetic  of  Europe.  The  seams  are  comparatively 
shallow  in  depth  and  vary  from  i  foot  to  12  feet  in  thickness. 

The  other  fields  of  Rhodesia  are  the  Mafungabusi  lying  just  north- 
east of  the  Wankie  field,  the  Lufua  and  Losita  about  50  miles  to  the 
northwest  of  the  latter  field,  and  the  Luano  some  75  miles  east  of 
Broken  Hill,  on  the  railroad  line.  A  small  field  near  Tuli  lies  about 
150  miles  southeast  of  Bulawayo,  and  another  on  the  Sabi  River, 
near  Sabi,  225  miles  southeast-by-east  from  Bulawayo.  These  two 
fields  are  not  on  a  railroad.  It  is  supposed  that  a  concealed  field 
lies  beneath  the  Victoria  Falls  basalts.  The  largest  number  of  seams 
explored  is  in  the  Luano  field  where  four  have  been  found  reaching 
an  aggregate  thickness  of  almost  18  feet.  The  thickest  single  seam 
is  in  the  Wankie  field  and  it  runs  up  to  12  feet.  The  ash  in  the 
Rhodesian  coals  is  high  like  that  in  the  coals  of  South  Africa,  most 
of  them  running  over  13  per  cent. 

Belgian  Congo.  —  In  the  Belgian  Congo  there  are  two  coal  fields 
according  to  Renier,  known  as  the  Lukugo  and  Lualabo.  The  coals 
in  the  former  field  are  regarded  as  of  Permo-Carboniferous  age  and 
there  are  three  flat-lying  seams  running  over  10  feet  in  thickness. 
The  coal  is  much  lower  in  ash  than  much  of  that  in  South  Africa. 
It  averages  around  10  per  cent.  In  the  Lualabo  field  the  coal  is 


UNION  OF  SOUTH  AFRICA  441 

probably  of  Triassic  age  and  there  are  several  seams  several  feet  in 
thickness.  It  is  of  inferior  quality,  however,  as  much  of  it  is  high  in 
sulphur  and  very  high  in  ash. 

Union  of  South  Africa.  —  The  coal  deposits  of  the  Union  of  South 
Africa  occur  in  the  Karroo  series  which  apparently  includes  rocks  of 
Carboniferous,  Permian  and  Triassic  ages  as  they  are  known  else- 
where. The  seams  usually  lie  within  200  feet  above  the  Dwyka 
formation,  the  basal  conglomerate  of  the  Karroo  series.  Much  of 
the  coal  is  undoubtedly  of  Permian  age  and  the  same  peculiar  plant 
associations,  usually  known  as  the  Glossopteris  or  Gangamopteris 
flora,  which  are  found  in  the  coal  measures  of  India  and  Australia, 
are  found  here  associated  with  the  glacial  deposits.  The  coal  is 
practically  all  of  the  bituminous  variety.  A  little  lignite  occurs  in 
Cretaceous  and  Tertiary  rocks  but  it  is  unimportant.  One  feature 
of  most  of  the  coal  is  the  high  ash  content  which  runs  from  6  to  30 
per  cent  and  averages  between  10  and  15  per  cent. 

Transvaal:  In  the  Transvaal  the  coal  seams  lie  quite  flat  and 
occupy  the  high  lands.  They  are  usually  of  shallow  depth,  those 
worked  being  less  than  400  feet  deep.  Many  of  the  deposits  occupy 
rather  limited  and  isolated  basins  owing  to  the  topographic  con- 
ditions existing  when  they  originated.  They  are  also  associated 
with  coarse  sediments,  and  some  writers  have  considered  that  practi- 
cally all  of  the  South  African  coals  are  of  drift  origin,  but  in  certain 
places  stumps  and  roots  are  found  in  place  beneath  the  seams  indi- 
cating their  in  situ  origin.  In  the  Transvaal  the  main  field  is  the 
Witbank  or  Middleburg  and  in  it  there  are  five  known  seams,  giving 
an  aggregate  thickness  of  about  56  feet  of  coal.  The  average  thick- 
ness of  the  seams  worked  runs  around  10  feet,  the  maximum  reaching 
about  20  feet. 

Cape  of  Good  Hope  and  Natal:  In  these  provinces  as  in  the 
Transvaal,  the  coal  occurs  in  the  Karroo  series,  but  near  the  top. 
The  Dwyka  lies  at  the  base  of  the  Karroo  in  this  region  as  elsewhere 
in  South  Africa  and  includes  a  thick  glacial  till.  The  coal  occurs  in 
the  Molteno  beds  which  are  younger  than  the  beds  containing  the 
coal  in  the  Transvaal  and  they  are  apparently  of  Rhaetic  (Triassic) 
age.  The  mines  are  worked  by  adits  and  the  workings  are  confined 
largely  to  the  portions  of  the  seams  near  the  outcrops,  because  many 
of  the  seams  have  been  so  broken  up  by  intrusions  of  igneous  rock 


442      THE   COAL   FIELDS  OF   THE   WORLD— AFRICA  AND   OCEANIA 

that  their  extent  is  uncertain.  Much  of  the  coal  has  been  devolati- 
lized  and  anthracitized  by  the  heat  of  these  intrusions.  A  consider- 
able amount  of  the  coal  is  semianthracite  and  it  is  high  in  ash,  usually 
above  20  per  cent.  It  is  low  in  sulphur  but  a  large  amount  of  clinker 
is  produced  and  it  is  said  that  this  clinker  is  taken  care  of  on  the 
locomotives  by  specially  designed  fireboxes.  There  are  some  beds 
of  lignite  of  Tertiary  age  but  they  are  not  of  much  importance. 

In  Natal,  the  coal,  which  is  similar  to  that  in  the  Cape  of  Good 
Hope  Province,  has  been  extensively  intruded  by  igneous  rocks  and 
to  quite  an  extent  converted  into  semianthracite.  Many  of  the 
mines  are  sufficiently  gaseous  to  require  the  use  of  safety  lamps. 

The  coal  industry  in  Africa  is  very  young  and  much  will  be  added 
in  the  coming  years  to  our  knowledge  of  the  geology  and  the  coal 
resources  of  the  continent.  From  the  general  character  of  the  ge- 
ological conditions  on  the  continent,  however,  it  seems  improbable 
that  Africa  will  ever  be,  comparatively  speaking,  a  great  coal-produc- 
ing continent. 

Oceania1 

Oceania  includes,  for  the  purposes  of  this  discussion,  the  continent 
of  Australia  and  the  islands  of  New  Zealand  and  Tasmania. 

Australia's  reserves  of  high-grade  coal  are  considerable,  although 
they  are  smaller  than  those  of  Great  Britain  and  very  small  compared 
with  those  of  the  United  States  or  Canada,  two  countries  to  which 
Australia  is  almost  equal  in  size.  The  table  given  below  shows  the 
estimated  reserves  for  New  Zealand  and  the  various  states  of  Aus- 
tralia. The  latter  country  holds  the  record  for  the  thickest  coal 
seams  in  the  world.  There  are  two  seams  of  brown  coal  in  Victoria, 
which  are  266  and  227  feet,  respectively,  in  thickness. 

1  For  comprehensive  reports  see  The  Coal  Resources  of  the  World,  Vol.  I.  Also 
Coal-fields  and  Collieries  of  Australia  by  F.  Danvers  Power  (Critchley  Parker).  Hand- 
book for  Australia,  British  Assn.  Adv.  Sci.  1914.  Reports  of  the  various  state  Geolog- 
ical Surveys  and  Departments  of  Mines. 


ioa 


no 


COAL  AREAS  OF  OCEANIA 

SCALE  OF  MILES 

100500  200          400          600          800 

Tertiary  Coals 


170 


ON 
ISLANDS 


&NE.W 


,0 

FIJI  ISLANDS  Cx? 

VETI 

o 


20 


NEW 
CALEDONIA1 


NORT 
Auck 


North  Cape 

k 


ISLAN 


Bast 
Cape 


sou 
N 

ISLAND 


NEW 


Blen-y?"™'61"11**011 
Hr«hein7% 

ZEALAND 


tchurch 


Dunedin 


U0°    from         Greenwich    150 


& 


OCEANIA 


443 


iCOAL  RESOURCES  OF  OCEANIA 
(In  millions  of  metric  tons,     i  metric  ton  =  1.1023  short  tons.) 


Actual  Reserve 

Probable  Reserve 

Class  of  Coal 

Class  of  Coal 

Total 

A 

B  and  C 

D 

A 

BandC 

D 

Anthracite 
and  some 

Bituminous 

Brown 
coals  and 

dry  coals 

lignites 

Australia: 

New  South 

Wales 

B      118.4.30 

Victoria  

B         40 

B                       12 

3I»H4 

Queensland.  .  . 

99 

B     1766 

66 

<;6o 

B        ii,on 

800 

C       165 

C             7Si 

West  Australia 

153 

500 

Tasmania  

B               65 

C                i 

99 

1971 

219 

560 

130,279 

32,H4 

165,242 

New  Zealand  .  .  . 

B         26 

612 

B              99 

1,863 

C       363 

C            423 

3,386 

99 

2360 

•831 

560 

130,801 

33.977 

168,628 

1  These  figures  are  based  on  seams  I  foot  and  over  to  a  depth  of  4000  feet;  and  2  feet  and  over  between 
4000  and  6000  feet  in  depth.  Coal  Resources  of  the  World,  Vol.  I.  For  description  of  classes  of  coal,  see 
Classification  of  Coals,  Chapter  V. 

Geological  age  of  coals:  The  geological  ages  of  the  coals  in  Oceania 
vary  from  Carboniferous  to  Tertiary,  the  most  important  fields  being 
Permo-Carboniferous  (Permian).  The  latter  are  closely  related  to 
the  coal  deposits  of  India  and  South  Africa  and  to  some  of  those  of 
South  America.  These  deposits  are  characterized  by  the  same  pe- 
culiar plant  associations,  as  Gangamopteris,  Glossopteris  and  Rhacop- 
teris  are  among  the  outstanding  fossil  plants  of  the  Australian  coal 
measures.  Lepidodendron,  so  abundant  in  the  Coal  Measures 
throughout  the  rest  of  the  world  is  present  in  the  Devonian  and 
Carboniferous  rocks  in  Australia  but  absent  in  the  Permo-Carbon- 
iferous, as  the  violent  changes  in  climate  wiped  out  this  and  related 
genera  and  ushered  in  the  Glossopteris  flora.  The  same  interesting 
glacial  conditions  prevailed  in  Australia  in  the  Permo-Carboniferous 


ffU 


W>T  jBSiig 


oiog-  UJ9JTS8M.    _ 


444     THE  COAL  FIELDS  OF  THE  WORLD— AFRICA   AND  OCEANIA 

as  in  India  and  South  Africa  and  the 
same  difficulty  is  experienced  in  trying 
to  separate  the  Carboniferous  from  the 
Permian. 

The  other  geological  systems  carrying 
important  coal  seams  are  the  Triassic 
in  Tasmania,  the  Jura-Trias  in  Queens- 
land, the  Upper  Cretaceous  in  Queens- 
land and  New  Zealand,  the  Miocene 
in  Victoria  and  the  Tertiary  in  New 
Zealand.  The  rank  of  the  coal  varies 
from  bituminous  and  anthracite  in  the 
Permo- Carboniferous  to  bituminous  and 
lignite  in  the  Mesozoic  and  lignite  in  the 
Tertiary  formations. 

New  South  Wales.1  —  The  coals  of 
this  state  are  of  high  grade  and  are 
bituminous  in  rank.  They  are  valuable 
as  gas,  domestic  and  steaming  coals. 
Much  of  the  coal  is  of  good  coking 
quality.  There  are  four  important 
fields,  the  Maitland,  Newcastle,  Illa- 
warra  or  Southern,  and  the  Lithgow  or 
Western  field.  The  coal  in  all  these 
fields  is  of  Permo-Carboniferous  age  and 
the  strata  are  divided  as  follows,  in 
descending  order: 

Thickness 
in  feet. 

(1)  Upper  or  Newcastle  Coal  Measures 

with  twelve  seams  of  coal  varying 
from  3  to  25  feet  in  thickness  with 
aggregate  of  35  to  40  feet  work- 
able coal.  Glossopteris  predom- 
inates over  Gangamopteris. .  .  1400-1500 

(2)  Dempsey  series.     Fresh  water  de- 

posits without  coal 2200 

(3)  Middle,  or  Tomago,  or  East  Mait- 

land  Coal    Measures  with    six 

1  Pittman,  E.  F.,  The  mineral  resources  of  New 
South  Wales,  1913. 


.s 


VICTORIA  445 

Thickness 
in  feet. 

seams  of  coal  3  to  7  feet  in  thickness  and  aggregating  18  feet  of 

workable  coal 500-1800 

(4)  Upper  Marine  series  with  glacial  erratics  in  shales 6400 

(5)  Lower  or  Greta  Coal  Measures  with  approximately  20  feet  of  work- 

able coal  in  two  seams,  the  Upper  seam  14  to  32  feet  thick  and  the 

Lower  seam  3  to  1 1  feet  thick.  100-  300 

(6)  Lower  Marine  series,  containing  much  igneous  rock  and  beds  of  glacial 

till  at  base.  The  rocks  of  the  Carboniferous  system  are  marine 
and  fresh- water  sediments  with  an  abundance  of  igneous  rock,  and 
in  parts  of  Australia  are  20,000  feet  thick.  They  are  not  coal-bear- 
ing. 

The  Newcastle  field  has  been  the  most  important  producer  in 
the  state  but  many  of  its  collieries  are  already  exhausted.  In  some 
places  the  mines  extend  beneath  the  sea.  Some  seams  have  been 
intruded  with  granite  which  has  produced  natural  coke  and  nigger- 
head  coal.  In  the  Illawarra  and  Lithgow  fields  the  coal  occurs  in 
the  Newcastle  series.  This  series  is  continuous  from  Newcastle  to 
Illawarra  and  again  from  Sydney  westward  to  Lithgow.  At  Sydney 
Harbor  the  upper  seam  is  worked  at  a  depth  of  2882  feet. 

New  South  Wales  contains  a  large  amount  of  oil  shale  known  in 
Australia  as  kerosene  shale  and  resembling  the  Torbanite  of  Scot- 
land. The  seams  occur  as  lenses,  sometimes  reaching  about  a  mile 
in  extent,  and  from  a  few  inches  to  about  4  feet  in  thickness.  They 
are  of  Permo- Carboniferous  age  and  the  organic  matter  in  them 
comes  from  the  spores  of  plants. 

Queensland.  —  This  is  the  second  most  important  state  in  Aus- 
tralia in  coal  reserves.  The  coal  is  almost  all  bituminous  except  a 
few  million  tons  of  semianthracite  in  the  Dawson  River  field.  There 
is  some  lignite,  but  this  is  of  comparatively  little  importance.  The 
coals  are  mostly  of  Permo-Carboniferous  age,  although  the  bulk  of 
the  coal  so  far  worked  is  Jura-Trias  in  age.  The  Burrum  field  is 
considered  to  be  of  Cretaceous  age,  probably  Lower  Cretaceous. 
The  Blair  Athol  field  carries  a  seam  of  good  clean  coal  66  feet  thick 
at  a  depth  of  only  120  feet  below  the  surface.  This  coal  is  Permo- 
Carboniferous  in  age. 

Victoria.  —  The  coal  resources  of  Victoria  have  not  been  very 
fully  determined.  There  is  some  bituminous  coal  of  Jurassic  age 
but  the  main  reserves  are  in  the  Miocene  brown  coal  and  the  thick- 


446      THE   COAL  FIELDS  OF  THE  WORLD— AFRICA  AND   OCEANIA 

est  seams  known  occur  in  this  state.  At  Morwell  a  bore  hole  passes 
through  780  feet  of  brown  coal  in  a  depth  of  1010  feet  of  strata  and 
there  are  three  very  thick  seams  running  266,  227  and  166  feet,  re- 


FIG.  141.  —  Thick  series  of  Coal  Measures  on  coast  of  New  South  Wales,  at  Shep- 
herd's Hill.     (Photo  by  E.  S.  Moore.) 

spectively.  This  coal  averages  35.08  per  cent  water;  29.24  per 
cent  volatile  matter;  33.28  per  cent  fixed  carbon;  and  2.40  per  cent 
ash.  It  can  no  doubt  be  used  for  briquetting  and  in  gas  producers. 


WESTERN   AUSTRALIA 


447 


Tasmania.  —  Permo- Carboniferous  coal  in  thin  seams  and  high 
in  sulphur  has  been  mined  a  little  for  domestic  purposes  in  the  Mer- 
sey and  Preolenna  coal  fields.  Most  of  the  coal  mined  comes  from 
the  Triassic  formations  which  have  suffered  much  faulting  and  which 
have  also  been  much  disturbed  by  intrusions  of  igneous  rock.  The 
coal  is  high  in  ash  and  it  is  not  used  much  except  for  domestic  pur- 
poses and  on  some  of  the  railroads.  Two  collieries  are  at  work 
near  St  Mary's  and  they  together  produce  about  60,000  tons  a  year. 

Considerable  oil  shale,  known  as  Tasmanite  shale,  is  found  on 
the  island  and  it  is  said  to  yield  40  to  50  gallons  of  crude  oil  per  ton. 


I 


FIG.  142.  —  Collieries  at  the  state  mine,  Port  Elizabeth,  New  Zealand.     (Photo 

by  E.  S.  Moore.) 

Western  Australia.  —  The  only  productive  field  in  this  state  is 
the  Collie  field  lying  south  of  Perth.  This  field  is  a  block  of  Permo- 
Carboniferous  measures  about  50  square  miles  in  extent.  It  lies  at 
quite  a  shallow  depth  and  is  little  folded  or  faulted  although  surrounded 
by  faults,  one  on  the  southwest  having  a  throw  of  about  2000  feet. 
The  coal  is  friable,  non-coking,  subbituminous  to  bituminous  in  rank 
and  partly  of  the  splint  variety.  It  has  a  high  moisture  content. 
The  low  fuel  ratio  of  the  coals  in  the  Collie  field  is  due  to  the  lack 
of  pressure  exerted  on  these  beds  even  though  they  occur  in  for- 
mations as  old  as  the  Permo-Carboniferous. 


448      THE    COAL  FIELDS   OF  THE   WORLD— AFRICA  AND   OCEANIA 

South  Australia  and  Northern  Territory.  —  South  Australia  con- 
tains some  Jurassic  coal  in  the  Leigh's  Creek  field,  and  a  small 
amount  has  been  mined.  It  is,  however,  of  poor  quality.  A  seam 
47  feet  thick  is  said  to  have  been  penetrated  at  a  depth  of  about 
1500  feet.  In  the  Great  Australian  Artesian  Water  Basin  lignite 
occurs  in  the  Lower  Cretaceous  and  in  the  southern  part  of  the  state 
lignite  of  Tertiary  age  occurs  in  a  number  of  places,  but  there  has 
been  little  exploitation. 

The  Northern  Territory,  so  far  as  known,  has  no  important  coal 
deposit. 

New  Zealand.1  —  New  Zealand  has  inadequate  fuel  supplies  for 
her  future  needs  as  at  the  present  rate  of  increase  in  production  her  bi- 
tuminous coal  will  be  exhausted  in  less  than  fifty  years.  Her  main  re- 
serve lies  in  the  Tertiary  brown  coals.  The  seams  are  notably  lenticu- 
lar in  form  and  they  occur  as  if  deposited  around  the  margins  of  basins. 
There  is  a  little  anthracite  in  the  South  Island,  in  the  folded  and 
faulted  areas  and  where  the  seams  have  been  intruded  by  igneous 
rocks,  but  the  quantity  is  very  small.  The  geological  age  of  the 
coal  runs  from  Jurassic  through  the  Upper  Cretaceous  and  the  Ter- 
tiary. Possibly  there  is  some  lignite  of  Pleistocene  age.  The  thick- 
nesses of  some  of  the  seams  are  as  follows:  50  to  60  feet  of  brown 
coal  in  the  Waikato  district  near  Auckland;  53  feet  of  bituminous 
coal  in  the  Buller-Mokihinui  district;  and  80  feet  of  lignite  in  Central 
Otago.  As  stated  above,  however,  the  seams  are  very  irregular 
in  thickness,  and  they  are  commonly  lenticular  in  outline. 

Antarctica 

T.  W.  E.  David2,  who  spent  considerable  time  in  Antarctica  on 
geological  work  with  the  Shackleton  expedition,  states  that  the  coal- 
bearing  rocks  in  this  great  continent  may  cover  something  less  than 
12,000  square  miles.  Coal  has  been  found  at  the  head  of  Beard- 
more  Glacier  and  at  Mackay  Glacier,  605  geographical  miles  Epart. 
The  coal-bearing  area  is  a  long,  narrow  "  horst "  bounded  by  large 
faults.  As  many  as  six  seams  with  22  feet  of  coal  have  been  seen. 
The  enclosing  rocks  are  believed  to  be  of  Permian  age  and  the  coals 
are  therefore  related  to  those  of  Australia. 

1  Marshall,  P.,  Geology  of  New  Zealand,  Wellington,  N.  Z.,  1912. 

2  Coal  Resources  of  the  World. 


INDEX 

Numbers  refer  to  pages.    Illustrations  are  indicated  by  an  asterisk  after  page  numbers. 


Africa:   coal  fields  of,  438;   coal  resources, 

table  of,  438;   geological  age  of  coals  of, 

439;  map  of,  437. 
Ala-Kool,  algae  in,  176. 
Alaska:   coal  fields  of,  397;   coal  resources 

of,  400;    entry  on  Coal  Lands  of,  240; 

lignite  from,  83;*  map  of,  399. 
Alaskan   coals,    stratigraphic   position   of 

398. 

Alberta,  coal  in,  343. 
Alethopteris  serli,  205.* 
Algae,  186;  ia  bogheads,  175. 
Alkalies  in  coal,  37. 
Allegheny  formation,  section  of,  367. 
Allen,  A.,  290. 

Allen  Shaft,  Pictou  coal  field,  341.* 
Alliance  Breaker,  304.* 
Allochthonous,  124,  129. 
Ambrite,  102. 
American   Society  for  Testing  Materials, 

44- 

Andreaeales,  188. 

Andre's  rule  for  shaft  pillars,  276. 

Andrews,  E.  B.,  128. 

Andros,  S.  O.,  305;  illustration  by,  283. 

Angers,  81. 

Angiosperms,  184,  185,  206;  first  appear- 
ance of,  213. 

Annularia,  198,  193.* 

Antarctica,  coal  deposits  in,  448. 

Anthracite,  81,  94,  93;*  market  sizes  of, 
301;  of  Keboa.,  81;  specific  gravity  of, 
4;  standards  of  preparation  of,  302; 
anthracite  mine  model,  274;*  anthra- 
cite mining  in  Pennsylvania,  277;  an- 
thracite region  of  Pennsylvania,  363. 

Anthrax,  n. 

Anthrocoal,  326. 

Anticline,  222. 


Anticlinorium,  223. 

Apparent  specific  gravity,  7. 

Araucarian  pines,  211. 

Arber,  E.  A.  N.,  154,  156. 

Arctic  islands,  coal  in,  351. 

Arctic  tundra,  132. 

Argentine  Republic,  coal  in,  405. 

Arizona,  coal  in,  387 

Aristotle's  Meteorology,  2. 

Arkansas:  coal  in,  385;  section  of  forma- 
tions of,  385. 

Ash  determination,  50. 

Ashes:  from  coal,  composition  of,  52; 
fusibility  of,  53,  121;  from  trees,  compo- 
sition of,  38. 

Ashley,  G.  H.,  89,  95,  147,  148,  255,  262, 
370,  378,  381,  382. 

Ashley's  Use  Classification,  118. 

Ashmead,  D.  C.,  302;  illustration  by, 
304- 

Asia:  coal  fields  of,  429;  coal  resources, 
table  of,  430;  map  of,  PI.  XVIII. 

Asiminia  triloba,  157. 

Asterophyllites,  198,  193.* 

Australia:  coal  resources  of,  443;  mining 
methods  in,  288. 

Austria:  coal  fields  of,  423;  coal  resources 
of,  409. 

Autochthonous,  124,  129. 

Autun,  bituminous  schists  of,  175. 

Bacilli,  159.* 

Bacteria  in  coal,  158.* 

Bailey,  E.  G.,  43. 

Bain,  H.  F.,  263. 

Bald  cypress,  211. 

Balfour,  174. 

Barnes,  C.  R.,  186. 

Barrier  pillars,  273;  rule  for  size  of,  275.. 


449 


450 


INDEX 


Barsch,  O.,  12. 

Bathvillite,  103. 

Battery,  279. 

Battery  breast,  279.* 

Baumhauer,  E.  H.  V.,  70. 

Baxton  megaspores,  14.* 

Bayley,  F.,  307. 

Beard,  J.  T.,  290. 

Beaver,  Pa.,  Quadrangle,  structure  sec- 
tion of,  366. 

Bedson,  P.  P.,  21. 

Beehive  coking,  318. 

Beehive  ovens,  319.* 

Belgian  Congo,  coal  in,  440. 

Belgium:  coal  fields  of,  420;  coal  resources 
of,  408;  structure  section  in,  420. 

Bell,  220. 

Bennettitales,  207. 

Bernice  Field,  367. 

Beroldingen,  Franz  von,  n,  126. 

Bertrand,  C.  E.,  12,  174,  175,  176;  illus- 
tration by,  175. 

Bethune,  81. 

Bevan,  J.  P.,  168. 

"Big"  seam  at  Pocahontas,  376.* 

Biochemical  process,  158. 

Bird,  E.  H.,  320. 

"Bird's  eye"  coal,  94. 

Bituminous  coal,  87,  85;*  photomicro- 
graph of,  12;  preparation  of,  305;  spec- 
ific gravity  of,  4. 

Bituminous  schists  of  Autun,  175. 

Black    Creek    seam,    photomicrograph   of  ' 
coal  from,  16. 

Black  damp,  291. 

Black  lignite,  84,  86. 

Blairmore-Frank  region,  structure  sec- 
tion of,  346. 

Blandy,  J.  F.,  217. 

Blind  shaft,  267. 

Block  longwall  system,  284.* 

""Blossom,"  242. 

Blowers,  gases  from,  25. 

Blumenbach,  84. 

Bogheads,  87;  origin  of,  174;  phosphor- 
ous in,  36. 

Bolivia,  coal  in,  404. 

Bomb  calorimeter,  72;  for  sulphur,  59. 

Bontchew,  G.,  425. 


Borlkjof,  J.  C.  B.,  404. 

Borntrager,  20. 

Bosnia  and  Herzegovina;  coal  fields  of, 
424;  coal  resources  of,  409. 

Botryococcus  braunii,  176. 

Boulets.  310. 

Boulton,  W.  S.,  264. 

"Bound"  molecules,  21. 

Bousquet,  G.,  407. 

Bownocker,  J.  A.,  77,  370. 

"Brasses,"  34. 

Brazil,  coal  in,  405. 

Breaker;  cross-section  of  the  Alliance, 
304;  the  Loree,  306.* 

Breaking  coal  at  face,  284. 

Break-throughs,  270. 

Breasts,  267,  271,  278. 

British  Columbia,  coal  in,  348. 

British  North  Borneo,  coal  in,  434. 

British  thermal  unit,  (B.t.u.),  71. 

Brongniart  A.,  84,  194,  202. 

Brooks,  A.  H.,  397;  illustration  by,  399. 

Brooks,  G.  S.,  312. 

Brownsville,  Pa.,  Quadrangle,  structure 
section  of,  366. 

Brunton's  slope  chart,  250. 

Brushing  down,  269. 

Bryales,  188. 

Bryophytes,  186,  188. 

Buckland,  W.,  126. 

Buffon,  L.,  126. 

Buggy  system,  278. 

Bulgaria:  coal  fields  of,  425;  coal  re- 
sources of,  408. 

Bulman  and  Redmayne,  264. 

Butts,  Charles,  illustration  by,  378. 

Bureau  of  Mines  Method  of  determination 
of  specific  gravity,  5. 

Burgess,  M.  J.,  26,  27,  28. 

"Buried  forests,"  138. 

Burrell,  G.  A..  291,  293. 

Byerite,  91. 

By-product  coking,  320. 

By-product  derivatives,  323. 

By-product  tests  on  various  coals,  28. 

Byron,  T.  H.,  320. 

Cahaba  Coal  Field,  structure  section  of, 
378. 


INDEX 


451 


Caking  coal,  87. 

Calamarieae,  198. 

Calamites,  198,  195,*  194.* 

Calcareous  concretions,  230. 

Calcium  in  coal,  37. 

Calcium  oxalate,  20. 

California,  coal  in,  395. 

Calorie,  71. 

Calorific  value:  calculated,  79;  deter- 
mination of,  71. 

Calorimeter:  standardization  of,  77;  va- 
rious types  of  .bomb,  72;  calorimeter 
washings,  75. 

" Camel-backs,"  220. 

Campbell,  J  R.,  306. 

Campbell,  M.  R.,  42,  44,  84,  86,  169, 
363,  368,  375,  395. 

Campbell's  classification,  106. 

Canada:  coal  resources  of,  339;  map  of, 
PI.  XI. 

"Candle "coal,  89. 

Canmore,  Alberta,  347.* 

Cannel  coal,  87,  89;  origin  of,  174;  photo 
micrograph  of,  90;  specific  gravity  of, 
4,  , 

Canneloid,  n. 

Cape  of  Good  Hope,  coal  in,  441. 

Carbocoal,  326. 

Carbon,  determination  of,  63. 

Carbon  dioxide,  22,  291. 

Carbon-hydrogen  ratio  and  depth,  dia 
gram  of,  167. 

Carbonite,  98.* 

Carbon  monoxide,  22,  292;  detector  of, 
294;  effect  on  animals  of,  293.  * 

Carnegie,  Pa.,  Quadrangle,  structure 
section  of,  366. 

Carnot,  Ad.,  36,  55,  70,  80. 

Cellulose,  18. 

Cement  burning  coals,  313. 

Central  America,  coal  fields  of,  401. 

Central  Coal  Basin  rule  for  shaft  pillars, 
276. 

Ceratizamia  mexicana,  37. 

Chain  pillar,  273. 

Chamberlin,  R.  T.,  20,  22. 

Chamberlin,  T.  C  ,  155. 

Chamber  longwall,  284. 

Chambers,  267,  271. 


Chance,  H.  M.,  25 

Charbon,  2. 

Chemical  analysis,  40. 

Chemical  properties  of  coal,  18. 

Cherry  Coal,  87,  88. 

Chile,  coal  in,  406. 

China:   coal  fields  of,  431;   coal  resources 

of,  430. 

Chlorine  in  coal,  37. 
Choke  damp,  291. 
Christopher,  J.  E.,  320. 
Church,  A.  H.,  86. 
Chutes,  278. 
Cincinnati  arch,  151. 
Clanney,  296. 
Clark,  A.  H.,  27,  31. 
Clark,  H.  H.,  296. 
Clark,  W.  B.,  372. 
Clarke,  F.  W.,  19,  20. 
Classification:    difficulties  in,  3;    of  coal 

lands,  260;  of  coals,  105;  of  plants,  184. 
Clay  veins,  214,  216,  215.* 
Cleats,  8. 

Climatic  conditions,  155. 
Coal:    amount   derived   from   peat,    148; 

color   of,    8;     defined,    2;     estimate   of 

quantity  in  seam  of,  258;  origin  of  word, 

2. 

Coal  apples,  229. 
Coal  balls,  229,  233. 
Coalification,  second  stage  of,  160. 
Coal  Measure  plants,  composition  of,  161. 
Coal  Miner's  Pocketbook,  264. 
Coal  provinces,  355. 
Coemans,  E.,  196. 
Cohen,  J.  B.,  21. 
Coke,   88;    for  domestic  fuel,  325;    and 

coking,  315. 
Coke  breeze,  323. 
Cokedale  Mine  natural  coke,  99. 
Coking  coal,  30,  87;  coking  coals,  316. 
Col.,  2. 

Cole,  B.  A.  J.,  416. 
Coleman,  A.  P.,  157. 
Collier,  A.  J.,  385. 
Collier's  classification,  106. 
Colloidal  fuel,  314. 
Colombia,  coal  in,  402. 
Colorado,  coal  in,  388. 


452 


INDEX 


Combustion  furnace,  63. 

Commentry  Basin,   36;    drifted   material 

in,   142;     fish  remains  in  coal  of,   18; 

open  cut  of,  287.* 
Competent  beds,  170,  223. 
Composition  of  wood,  peat,  and  coals,  96. 
Concretions  in  coal,  229. 
"  Condensed  "  gases,  26. 
Conemaugh  formation,  section  of,  368. 
Coniferales,  211. 
Connellsville  basin  coke,  99. 
Connellsville  coal  tested,  28. 
Constance,  Lake,  peat  on,  147. 
Contiguous  seams,  working  of,  280.* 
Contorted  partings,  224. 
Contours,  structural  and  surface,  248.* 
Coppee  oven,  320. 

Cordaitales,  208,  209;*  in  Devonian,  182. 
Cost  of  mining,  average,  per  ton,  257. 
Coulter,  J.  M.,  186. 
Cowles,  H.  C.,  1 86. 
Crane,  W.  R.,  384;    illustration  by,  83, 

100,  223. 

Critical  level,  136. 
Cross  and  Bevan,  161. 
Cross-cuts,  270;  cross-entries,  269. 
Crowsnest  coal  area,  map  of,  345. 
Cryptogamic  plants,  spores  of,  9. 
Curtis^  H.  A.,  326. 
Cut-out,  214;   215;*  on  Des  Moines  River, 

216. 

Cut-throughs,  273. 
Cycadales,  207. 
Cycadeoidea  marshiana,  208.* 
Cycadofilicales,  206. 
Cycadofilices,  203. 
Cycads,  Age  of,  184,  208. 

Dakotas,  coal  fields  of,  393. 
Dalburg,  F.  A.,  435. 
Dana,  E.  S.,  2,  3,  89,  91. 
Daubr'e,  A.,  101,  166. 
David,  T.  W.  E.,  156,  448. 
Davis,  C.  A.,  131. 
Davy,  Sir  William,  296. 
Dawson,  J.  W.,  12,  174,  209. 
"Debris,"  n. 
Defline,  M.,  416. 
Degousee,  M.  J.,  140. 


De  la  Becke,  166. 

De  Lisle,  87. 

Delta  deposits,  coal  in,  139. 

Denmark:  coal  fields,  of  421;  coal  re- 
sources of,  408. 

Denoel,  L.,  420. 

DePapp,  C.,  424. 

Depth:  maximum  of  coal  mines  in  foreign 
countries,  253;  maximum,  of  coal  mines 
in  the  United  States,  251;  of  burial, 
166;  of  seam,  determination  of,  247; 
table  for  determination  of,  249. 

Derivatives     of     coal     and     their     uses, 

Fig-  5. 

Descloizeaux,  A.,  97. 
Devonian  period,  first  appearance  of  land 

plants  in,  179. 
Diatoms,  86. 
Dike,  228,*  231.* 
Diller,  J.  S.,  396. 
Dip,  221.* 
Dismal  Swamp,   139,*  141,*  142;*    Lake 

Drummond    in,    137;*     map    of,    135; 

peat  in,  137. 

Displacement  in  fault,  225. 
Distillation,  products  of,  25. 
Domestic  anthracite,  preparation  of,  300. 
Dominian,  L.,  425. 
Dopplerite,  83. 
Dorrance,  C.,  310. 
Double  battery  breast,  279.* 
Double  room,  272.* 
Douglas,  E.  A.,  435. 
Dowling,   D.   B.,  339,  348;    classification 

by,  112;  illustration  by,  345,  346. 
Drake,  N.  F.,  431. 
Drift,  266. 

Drifted  vegetation,  139. 
Drills  in  prospecting,  243. 
Dron's  rule  for  shaft  pillars,  275. 
Dry  coal,  92. 
Dulong's  formula.  79. 
Dumble,  E.  T.,  99,  386. 
Duncan,  W.  G.,  291. 
Dunkard  formation,  section  of,  370. 
Dunkley,  W.  A.,  312. 
Durley,  R.  J,  7,  8,  339. 
Dutch  East  Indies,  coal  in,  435. 
Duxite,  103. 


INDEX 


453 


Dyer,  B.,  68. 
Dysodile,  86. 

Eastern-Middle  Anthracite  field,  section 
through,  362. 

Ecuador,  coal  in,  404. 

Electric  cap  lamp,  296. 

England:  coal  resources  of,  408;  resources 
of  various  coal  fields  in,  412. 

Entries,  263,  270. 

Equisetales,  190,  198. 

Equisetum,  198. 

Eschka  method  for  sulphur,  56 

Eshereck,  George,  Jr.,  327. 

Ethane  in  coal,  20. 

Europe:  coal  fields  of,  407;  coal  resources, 
table  of,  408;  map  of,  PL  XVI;  min- 
ing methods  in,  287;  geological  age  of 
coals  of,  410. 

Evans,  J.  W.,  434. 

Exposure  before  burial,  162. 

Face,  271. 

Face  on,  272. 

Falkenau,  brown  coal  of,  20. 

Fat  coal,  92. 

Fats,  composition  of,  20. 

Faults,  224,  225,*  226. 

Fayol,  H.,  32,  129,  141,  162. 

Federal  Trade  Commission  Report,  257. 

Ferns,  180,  201, 

Fieldner,  A.  C.,  44,  52,  70,  73 

Filicales;   see  Ferns. 

Finn,  C.  P.,  21. 

Fire  damp,  22,  294. 

First  mining  in  Virginia,  i. 

First  production  in  the  United  States,  i. 

Fish  remains  in  coal,  18. 

Fisher,  C.  A.,  251. 

Fixed  carbon,  determination  of,  56 

Flow,  igneous,  229. 

Flow  sheet  of  Alliance  Breaker,  303. 

Fontaine,  W.  M.,   184,  193;    and  White, 

illustration  by,  204. 
"Fool's  gold,"  34. 
Foot-acre,  value  of,  255. 
Formula  for  composition  of  coals,  149. 
Fossil  flora  of  coal-forming  periods,  178. 
Foster's  rule  for  shaft  pillars,  276. 


Foundry  coke,  standard  for,  316. 

Fracture  in  coal,  8. 

France:  coal  fields  of,  416;   coal  resources 

of,  408. 

Frank,  Alberta,  landslide,  344.* 
Franke,  G.,  309. 
Frazer,  J.  C.  W,  31. 
Frazer,  T.,  306. 
Frazer's  classification,  105. 
"Free"  paraffins,  21. 
Fremy,  E.,  30. 
Fresh  water  swamps,  133. 
Fuel   ratios   of   Pennsylvania   coals,   map 

of,  172 

Fundamental  matter,  n. 
Fungi,  1 86;  in  coal,  159. 
Fusain,  100,  307. 
Fusibility:    of  ash,   121;    of  various  coal 

ashes,  53. 

Gagates,  2,  97. 

Gamba,  F.  P.,  402. 

Gangamopteris,  180;   211.* 

Gangamopteris  flora,  156. 

Gangways,  267,  278. 

Garcia,  J.  A.,  290. 

Gardner,  J.  H.,  387. 

Gas  manufacture:  bibliography,  cited, 
25;  coals  for,  311. 

Gases:  evolved  from  coal  below  tempera- 
ture of  decomposition,  23;  in  coal,  22. 

Geikie,  A.,  147. 

Geographic  distribution  of  coal,  328. 

Geological  age  of  coals:  of  Africa,  439; 
of  Europe,  410;  of  North  America, 
table  of,  338;  of  Oceania,  443;  of  the 
United  States,  360. 

Geological  distribution  of  coal,  328;  by 
varieties,  table  of,  332. 

Geological  formations,  table  of,  330 

Georgia,  coal  in,  378. 

Germany:  coal  fields  of,  421;  coal  re- 
sources of,  409. 

Gibson,  378. 

Gingkoales,  210;  ancestors  of,  182. 

Glanzkohle,  94 

Glossopteris,  180,  211.* 

Glossopteris  flora,  156,  157. 

Gob  side,  272. 


454 


INDEX 


Gore,  N.  Z.,  retinite  from,  102. 

Gottlieb,  table  by,  161. 

Gouge,  225. 

Goutal,  M.,  79. 

Goutal's  curve,  80. 

Grains,  cones,  spores,  181.* 

Grains  from  Coal  Measures,  185.* 

Grande  Couche,  36,  214. 

Grand'Eury,  F.  C.,  128,  191,  203;  illus 
tration  by,  150,  181,  185,  209. 

Graphic  method  for  thickness,  244. 

Great  Britain;  coal  fields  of,  407;  coal  re- 
sources of,  408. 

Greece:  coal  fields  of,  425;  coal  resources 
of,  408. 

Gresley,  W.  S.,  130. 

Grinding  thin  sections,  15. 

Grout's  classification,  109. 

Gruner,  E.,  407;  classification  by,  115. 

Gr Liner,  L.,  128. 

Guignet,  E.  30. 

Gulf  Province,  385. 

Giimbel,  C.  W.,  von,  12,  128. 

Gymnosperms,  185,  206;  ancient  types  of, 
203;  dominant  in  Triassic,  182. 

Gypsum  in  coal,  35. 

Hade,  225. 
Hadley,  H.  F.,  31. 
"Half  on,"  272. 
Hall,  A.  A.,  21. 
Hall,  R.  D.,  36. 
Hamilton,  N.  D.,  309. 
Hapke,  L.,  32. 
Hard  coal,  94. 
Hardness,  8. 

Harper,  Francis,  illustration  by,  133,  134. 
Harrisburg,  111.,  coal  tested,  28. 
Haulage,  288;  electric,  290.* 
Hausmann,  J.  F.  L.,  84,  87. 
Hauy,  94. 

Hazeltine,  illustration  by,  373. 
Hazleton,  Pa.,  district,  95;   structure  sec- 
tion of,  362. 
Hawes,  G.  W.,  161. 
Hayden,  H.  H.,  433. 
Hayes,  C.  W.,  378. 
Headings,  267. 
Heat,  effects  of,  168. 


Heave,  225. 

Heavy  solutions  for  determination  of 
specific  gravity,  7. 

Heinrich,  O.  J.,  101. 

Hepaticae,  188. 

Hilaire,  B.  S.,  2. 

Hill,  R.  T.,  400. 

Hillman  Coal  and  Coke  Co.,  illustration 
by,  292,  319. 

Hinds,  H.,  382,  383. 

History  of  first  uses  of  coal,  i. 

Hochstetter,  102. 

Hoffman,  E.  J.,  31. 

Hogarth's  flask,  determination  of  specific 
gravity  by,  5.* 

Hoisting,  289. 

Holmes,  J.  A.,  42. 

Horn  Coal,  89. 

Horsebacks,  214,  216,  215;*  on  mine  map, 
218. 

Horsetails,  190;  silica  in,  37. 

Houille,  86,  87. 

Howarth,  384. 

Ho  well,  S.  P.,  298. 

Howley,  J.  P.,  352. 

Hughes'  rule  for  shaft  pillars,  276. 

Humboldtine,  20. 

Humic  coals,  87. 

Humus  acids,  20. 

Hungary:  coal  fields  of,  424;  coal  re- 
sources of,  409. 

Hutchinson  R.  P.,  illustration  by,  300, 
306. 

Hutton,  W.,  11,  174. 

Huxley,  174. 

Hydrogen,  295 ;  determination  of,  63. 

Hydrogen  sulphide,  295. 

Hydrogenous  coals,  90. 

Hydroxide  of  sodium  for  softening  sec- 
tions, 13. 

Igneous  intrusions,  228.* 

Illinois:     coal    in,    381;     section   of   Coal 

Measures  of,  380 
Illuminating  gas,  312. 
Inby,  271. 

Incompetent  beds,  170. 
India:    coal  fields  of,  433;    coal  resources 

of,  431- 


INDEX 


455 


Indian  Lands,  240. 

Indiana,  coal  in,  382. 

Inert  volatile  matter,  no. 

In  situ  theory,  124. 

Interior  province,  379. 

International  Geological  Congress,  classifi- 
cation by,  113. 

lonite,  104. 

Iowa:  cross-section  of  formations  of,  382; 
coal  in,  382. 

Ireland:  coal  fields  of,  416;  coal  resources 
of,  408;  peat  in,  133. 

Iron  in  coal,  37. 

Iso-anthracitic  lines,  173,  174;  of  South 
Wales  field,  165. 

Isoclinal  fold,  222. 

Isovols,  174. 

Italy:  coal  fields  of,  419;  coal  resources 
of,  408. 

Ivanov  S.  L.,  analysis  by,  177. 

Japan:   coal  fields  of,  432;    coal  resources 

of,  430. 
Jeffrey,  E.  C.,  12,  13,  101,  130,  174,  176, 

233;  illustration  by,  90. 
Jet,  97. 
John,  von,  20. 
Johnson,  W.  R.,  105. 
Johnston,  F.  W.,  103. 
Jones,  D.  T.,  21. 
Joseph,  1 66. 
Jukes,  J.  B.,  127;  illustration  by,  229. 

Kansas:    coal  deposits  in,  384;    structure 

section  of  Coal  Measures  of,  384. 
Karst,  84,  94. 
Katz,  S.  H.,  23. 
Katzer,  F.,  424. 
Kauri  gum,  102. 
Kaustobioliths,  130. 
Kelley,  W.  P,  38. 
Kentucky  cannel,  90. 
Kentucky,  coal  in,  377. 
Kerosene  shale,  175. 
"Kettle,"  220. 
Kick,  J.  J.,  196. 
Kidston,  203. 
Kilkenny  coal,  89. 
Kinosuke,  I.,  431,  432. 


Kirwin,  R.,  89. 

Kjeldahl-Gunning  method,  68. 

Klonne  oven,  322. 

Koppers  byproduct  coke  plant,  324.* 

Korea,  coal  in,  432. 

Krafft,  20. 

Kressman,  F.  W.,  32,  308. 

Le  Conte  J.,  127. 

Laccolith,  228. 

Land  Office  Regulations,  238. 

Land  plants,  rise  of,  180. 

Lane,  A.  C.,  379. 

La  Veta,  Colorado,  structure  section  near, 

388. 

Law  of  Hill,  1 66. 
Laws  governing  prospecting,  238. 
Leaf  cushions,  192. 
Leaf  traces  of  Sigillaria,  194. 
Leasing  laws,  240. 
Lenhart,  L.  R.,  52. 

Lepidodendron,  157,  180,  191;  179,*  183.* 
Lesher,  C.  E.,  51. 
Lesley,  J.  P.,  128. 
Lesquereaux,  illustration  by,  191,  193,  195, 

197,  200,  202. 
Lignite,  84;    ignition  temperature  of,  32; 

85;*   seam  of,  394;*   specific  gravity  of, 

4- 

Lignocellulose,  18. 

Liguria,  2. 

Link,  F.,  n,  126. 

Locating  new  seams,  242. 

Loew,  O.,  104. 

Logan,  W.  E.,  126. 

Loire  basin  coals,  31. 

Lonchopteris  bricei,  206.* 

"Long  horn,"  272. 

Longwall,  development  in   anthracite  re- 
gion, 285.* 

Longwall  method,  281. 

Longwall  mine,  282,*  283.* 

Lord,  N.  W.,  73,  77,  87. 

Loree  Breaker,  306.* 

Lump  anthracite,  301. 

Luster,  9. 

Lyburn,  E.,  416. 

Lycia,  jet  from,  2. 

Lycopodium,  190. 


INDEX 


Lycopods,  180. 
Lyes,  271. 

MacCulloch,  J.,  126. 

McCalley,  378. 

McCallie,  378. 

McConnell,  W.,  23,  24. 

McCreeth,  A.  S.,  106. 

Macklin,  J.  F.,  illustration  by,  290. 

Madura  arantiaca,  157. 

Macrosporangia,  207. 

Magnesium  in  coal,  37. 

Mallett,  E.  J.,  91. 

Maly,  102. 

Manchuria:  coal  fields  of,  432;  coal  re- 
sources of,  431. 

Mangrove  swamp,  N.  Z.,  144.* 

Mangrove  swamps,  138. 

Manitoba,  coal,  in  343. 

Map  of:  Africa,  437;  Alaska,  399;  Asia, 
PI.  XVIII;  Canada,  PI.  XI;  European 
Russia,  427;  Oceania,  PI.  XX;  South 
America,  403;  United  States,  PI.  XII; 
Western  Europe,  PI.  XVI. 

Marcasite,  34. 

Mariotte  flask,  65. 

Marsh  gas,  294. 

Marshall,  P.,  448. 

Marshes,  132. 

Martin,  G.  C.,  397. 

Maryland,  deposits  in,  372. 

Marzec,  L.,  424. 

Maumen?,  J.,  71. 

Mellite,  20. 

Merrimac  Mine  Breaker,  376.* 

Metagami  River  timber,  145.* 

Methane,  22,  294;  absorbed  by  coal,  23. 

Methyl  orange  indicator,  75. 

Mexico,  coal  in,  400. 

Meyer,  von,  24. 

Michado,  M.  R.,  406. 

Michigan:   coal  in,  379;   structure  section 

in,  379- 

Micrococcus,  159. 
Microscope  in  study  of  coal,  9,  n. 
Middletonite,  103. 
Mietzsch,  H.,  128,  138,  154. 
Miller,  B.  L.,  402. 
Miller,  C.  F.,  38. 


Mills,  J.  E.,  310. 

Milojkovitch,  F.  A.,  424. 

Mine  fires,  298. 

Mine  gases,  290;   relation  of,  to  volatile 

constituents,  25. 
Mine  level,  270. 
Mine  ventilation,  296. 
Mineral  charcoal,  100. 
Mineral  coal,  2. 

Mineral  constituents  of  coal,  33. 
Mineral,  defined  by  Dana,  3. 
Mineral  Industry,  cited,  321,  335. 
Mineral  Lands,  3,  238. 
Mineral  Resources  United  States  Geological 

Survey,  cited,  i,  255,  299,  353. 
Minimum  thickness  of  seams  mined,  253. 
Mining  Engineering  rule  for  shaft  pillars, 

276. 

Mining  machine  undercutting  ream,  289.* 
Mining  machines,  286. 
Mining  methods  in  foreign  countries,  287. 
Mining  of  coal,  264. 
Missouri,  coal  in,  383. 
Mitscherlich,  A.,  70. 
Moffat,  E.  S.,  164. 
Mohr,  F.,  145. 
Moh's  scale,  8,  95. 
Moissan,  H.,  32,  86. 
Moisture,  determination  of,  49. 
Moisture  oven,  49. 
Monoclinal  fold,  222. 
Monongahela  formation,  section  of,  369. 
Montana,  coal  in,  394. 
Montenegro,  425. 
Moore,  E.  S.,   217;    illustration  by,   144, 

145,  148,  152,  227,  231,  236,  265,  287, 

344,  351,  417,  446,  447. 
Morwell,  Australia,  214. 
"Mother-of-coal,"  100. 
Mourlot,  A.,  39. 
Mud-screen  product,  301. 
Muer,  H.  F.,  60 
"Mur,"  153. 
Murchison,  R.  L,  127. 
Musci,  1 88. 

Naked  seeds,  206. 
Naphthenes,  21. 
Natal,  coal  in,  447. 


INDEX 


457 


National  Parks,  240. 
Natural  coke,  98.* 
Neck,  271. 

Netherlands:    coal  fields  of,  420;    coal  re- 
sources of,  408. 
Neuropteris,  201,*  202.* 
Neuss,  84. 

New  Brunswick,  coal  in,  342. 
New  Mexico,  coal  in,  387. 
New  South  Wales,  coal  in,  444;    section 

through  main  coal  basin  of,  444. 
New  Zealand:    coal  fields  of,   448;    coal 

resources  of,  443. 
Newberry,  J.  S.,  128,  196. 
Newfoundland,  coal  in,  352. 
Niggerhead    coal,    230,    235;    analyses  of, 

237,  236.* 

Nitchie,  C.  C..  312. 
Nitric  acid,  effects  of,  on  coal,  30. 
Nitrogen  determination  of,  68. 
Non-caking  coal,  88. 
Non-coking  coal,  88. 
Normal  fault,  225. 
Norris,  R.  V.,  307. 
North  America:   coal  fields  of,  336;   coal 

resources    of,    337;     geological    age    of 

coals  of,  338. 

North  Dakota  lignite,  85.* 
Northern  Anthracite  field,  section  through, 

362. 

Northern  Great  Plains  Province,  387. 
Northern    Territory,    Australia,    coal    in, 

448. 

Northrup,  H.  B.,  analyses  by,  102. 
Northwest  Territories,  coal  in,  351. 
Nova  Scotia,  coal  in,  340. 
Norway,  coal  in,  428. 

Oak,  composition  of,  162. 

Oberfell,  G.  G.,  291. 

Occluded  gases  in  coal,  22. 

Oceania:  coal  fields  of,  438,  442;  coal 
resources,  table  of,  443;  geological  ages 
of  coals  of,  443 ;  map  of,  PI.  XX. 

Odell,  W.  W.,  312. 

Odontopteris,  200.* 

Ohio:  coal  in,  370;  section  of  Carbonifer- 
ous formations  of,  373. 

Oils,  composition  of,  20. 


Okefinokee  Swamp,  133,*  134.* 

Oklahoma,  coal  in,  385. 

Oleinic  acid,  177. 

Oliver,  F.  W.,  203,  204. 

Ombre  de  Cologne,  86. 

Ontario,  coal  in,  342. 

Ophioglossales,  190. 

Oregon:  coal  in,  396. 

Organic  acids,  salts  of,  20. 

Origin  of  coal,  123. 

Osbon,  C.  C.,  136. 

Otto-Hilgenstock  oven,  322. 

Otto-Hoffman  oven,  322. 

Outby,  271. 

Overthrust  fold,  222. 

Ovitz,  F.  K.,  22,  25,  26,  27,  28,  33,  309. 

Oxalic  acid,  20. 

Oxygen,  determination  of,  70. 

Oxypicric  acid,  30. 

Pacific  Coast  Province,  395. 

Packs;  gob,  282;  road,  282. 

Pack-walls,  282. 

Panel  system,  277.* 

"Paper  coals"  of  Russia,  20. 

Paraffin  series,  20. 

Parmelee,  C.  W.,  313. 

Parr,  S.  W.,  31,  32,  42,  43,  52,  60,  62,  70, 
79,  149,  308,  309;  classification  by,  109; 
peroxide  bomb  calorimeter  of,  67. 

Parrot  coal,  89. 

Partings,  214,  215.* 

Pas-de-Calais  coal  basin,  complicated  struc- 
ture in,  232.* 

Peacock  coal,  96. 

Peat,  82;  rate  of  accumulation  of,  146. 

Peat-bogs,  131. 

Pebbles  of  coal  in  Coal  Measures,  164. 

Pechkohle,  86. 

Pecopteris,  199.* 

Peek's  Handbook,  264,  300. 

Pennsylvania,  81;  bituminous  region  of, 
368;  coal  fields  of,  363;  structure  sec- 
tion through  southwestern  part  of,  366. 

Pennsylvania  anthracite:  distribution  of 
in  1917,  299;  specific  gravity  of,  96. 

Pennsylvania  bituminous  coal,  distribu- 
tion of  in  1917,  299. 

Permissible  explosives,  298. 


458 


INDEX 


Permo-Carboniferous  section  in  New  South 

Wales,  157,  444. 
Persia:   coal  fields  of,  434;    coal  resources 

of,  431. 

Peru,  coal'in,  404. 
Petrascheck,  W.,  423. 
Phanerogams,  206. 
Phenol  as  solvent  for  coal,  31. 
Philippine  Islands,  coal  in,  435 
Phillips,  W.  B.,  386. 
Phosphorous,    36;     determination    of,    in 

coal  ash,  53. 

Photometric  method  for  sulphur,  60. 
Photomicrographs  of  coal,  16;    from  Roy- 

alston  showing  spores  and  woody  tissue, 

10;    showing  pyrite,  35;    showing  resin, 

19;  showing  spores  in  cannel,  90. 
Phylloglossum,  190. 
Physical  constitution,  9. 
Physical  properties,  4. 
Pila  bibractensis,  175.* 
Pillar  drawing,  280 
Pillar-and-stall  system,  276. 
Pillars,  size  of,  273. 
Pinaceae,  211. 
Pinches,  215. 
Pines,  see  Pinaceae. 
Pinnularia,  198. 
Pishel,  M.  A.,  88. 
Pitch,  222. 
Pittman,  E.  F.,  444. 
Pittsburgh  seam,  369,  371,  372,  374,  375; 

photomicrograph  of  coal  from,  16. 
Plan  of  four-entry  mine,  268. 
Plankton  algae,  177. 
Plant  spores  used  in  distinguishing  seams, 

17- 

Pliny,  2. 

Pocahontas  coal  tested,  28. 

Pocahontas  field,  375. 

Poland,  coal  in,  426. 

Pollard,  W.,  7,  48,  63,  65,  69,  107,  166,  173. 

Pope,  G.  S.,  43- 

Port  Elizabeth,  N.  Z.,  collieries  of,  447.* 

Porter,  coal  of,  81. 

Porter,  H.  C.,  22,  25,  26,  27,  28,  33,  309. 

Porter,  J.  B,  7,  8,  339. 

Protugal:    coal   fields   of,   418;     coal   re- 
sources of,  408. 


"Pot",  220. 

Potonie,  H.,  12,  90,  130,  138. 
Pottsville  formation,  section  of,  367 
Powdered  fuel,  313. 
Powell,  A.  R.,  62,  317. 
Power,  F.  Danvers,  288,  442. 
Preparation  of  coal,  299. 
Pressure,  effect  of,  on  coal,  170. 
Prestwich,  J.,  97. 
Price  of  coal  at  mine,  256. 
Producer  gas,  311. 

Production  of  world  in  1913,  i;   by  coun- 
tries, 335;  and  states,  352. 
Prospecting  for  coal,  238. 
Proximate  analysis,  48. 
Psilo  tales,  190. 
Pteridophytes,  186,  188. 
Pycnometer,  4. 
Pyridine,  32. 
Pyrite,  34. 
Pyroretinite,  104. 

Queensland,  coal  in,  445. 

Rabino,  H.  L.,  434. 

Ranks  of  coal,  82. 

Rath,  G.  von,  analyses  by,  99. 

Reinchia  australis,  176. 

Renault  B.,  12,  148,  149,  174,  175,  196,  198, 

207;  illustration  by,  158,  159,  210. 
Renier,  A.,  420. 
Resinous  substances,  102. 
Resins:  composition  of,  20;  in  coal,  n. 
Resources  of  world  by  continents,  333. 
Retinite,  102. 
Rhacopteris,  180,  211.* 
Rhode  Island:   anthracite  of,  95;    coal  in, 

370- 

Rhodesia,  coal  in,  440. 
Rib,  271. 

Rice,  G.  S.,  287,  297. 
Richardson,   G.   B.,   illustration   by,   388, 

389- 
Ries,  H.,  172;    illustration  by,  341,  342, 

347,  376,  394- 
Riffle  sampler,  46. 
Rittman,  W.  F.,  25. 
Roberts  oven,  322. 
Robertson,  I.  W.,  291,  293. 


INDEX 


459 


Robinson,  W.  O.,  38. 

Rock  chutes,  280. 

Rock  Springs  coal  field,  structure  section 
of,  392. 

Rocky  Mountain  Province,  387. 

Roden,  J.,  434. 

Rogers,  H.  D.,  90,  92,  101,  127. 

Rolls,  214,  216,  215,*  234.* 

Ronchamp,  81 

Rooms,  267,  271;  inclined,  271.* 

Room-and-pillar  method,  264,  267. 

Royal  Commission  on  Coal  supplies,  253. 

Royalston,  111.,  photomicrograph  of  coal 
from,  10. 

Royalties  on  leases,  259. 

Roumania:  coal  fields  of,  424;  coal  re- 
sources of,  409. 

Russia:  coal  fields  of,  426;  coal  resources 
of,  409;  in  Europe,  map  of,  427. 

St.  £tienne:  fault  at,  227;*  tree  trunks 
near,  148,*  152.* 

Ste.  Colombe  sur  1'Hero,  97. 

Saar  basin,  section  through,  422. 

Safety  lamps,  295. 

Salisbury,  R.  D.,  155. 

Sampling,  40;  English  method  of,  48; 
equipment  for,  42;  in  laboratory,  47; 
laboratory  apparatus  for,  46;  standard 
method  of,  44. 

San  Raphael,  39. 

Sapropelic  coals,  90. 

Sapropelic  deposits,  130. 

Sargasso  Sea,  145. 

Saskatchewan,  coal  in,  343. 

Schering's  celloidin,  13. 

Schrotter,  104. 

Schulze,  Franz,  n. 

Schwarzkohle,  87. 

Scotland-  coal  fields  of,  413;  coal  re- 
sources of,  408. 

Scott,  D.  H.,  203,  204. 

Scouring  rushes,  198. 

"Seatearth,"  153. 

Seibert,  F.  M.,  293. 

Selvage,  225. 

Selvig,W   A,  52. 

Semet-Solvay  coke  pusher,  321.* 

Semet-Solvay  plant,  322.* 


Semianthracite,  92. 

Semibituminous  coal,  92. 

Sequoia,  211. 

Serbia:    coal  fields  of,  424;    coal  resources 

of,  409. 

Seyler's  classification,  107. 
Shaft,  266,  267. 
Shaft  bottom,  292.* 
Shaft  pillar,  273. 
Shaler,  N.  S,   135,  375;    illustration  by, 

i35,  137,  139,  Ui,  142. 
Shamel  Charles,  238. 
Shepherd's  Hill,  New  South  Wales,  446.* 
Sheppard,  S.  E.,  314. 
Sheridan  coal  tested,  28. 
Shoofly,  271. 
"Short  horn,"  272. 
Shove  fault,  226. 

Shultz  and  Lewis,  illustration  by,  392. 
Siberia,  coal  in,  431. 
Sidings,  271. 
Sigillaria,  180,  194,  187.* 
Sigillarian  cones,  195. 
Sigillariostrobus  goldenbergi,  189.* 
Silica  in  coal,  37. 
Sill,  228. 

Singewald,  J.  T.,  Jr.,  402. 
Sinnatt,  F.  S.,  307. 
Stele,  190. 

Slate  pickers  in  breaker,  300 .  * 
Slickenside,  225. 
Slip  fault,  226. 
Slope,  266. 
Smith,  G.  O.,  395. 
Smith  process,  327. 
Smithing  coals,  313. 
"Sole,"  153. 

Solms-Laubach,  193,  198. 
Solubility    of    coal,    29;     relation    of,    to 

coking,  30. 

Somermeier,  E.  E.,  77. 
Somme  Valley,  peat  in,  147. 
Sorus,  189. 

South  Africa,  Union  of,  coal  in,  441. 
South  America,  coal  fields  of,  402;     map 

of,  403 

South  Australia,  coal  in.  448 
South  Wales:  coal  in,  414;  origin  of  coals 

of,  1 68. 


460 


INDEX 


South  Wales  field,  diagram  of  ash  and 
carbon-hydrogen  ratios  of  coal  of,  173. 

Southern  Nigeria,  coal  in,  439. 

Spain,  coal  fields  of,  418;  coal  resources 
of,  408. 

Specific  gravity:  defined,  4;  of  anthracite 
4;  of  "ash-free"  and  "moisture-free" 
specimens,  7;  of  bituminous  coal,  4; 
of  cannel,  4;  of  lignite,  4;  relation  of, 
to  quality  of  coal,  8. 

Specific  gravity,  determination  of:  by 
Bureau  of  Mines,  5;  by  heavy  solutions, 
7;  by  Hogarth-flask,  5;  by  hydrometer 
method,  6;  by  pycnometer,  4. 

Spermatophytes,  185,  186,  206. 

Sperr,  F.  W.,  Jr.,  320. 

Sphagnum  132,  188. 

Sphenophyllales,  196. 

Sphenophyllum,  190. 

Sphenopteris,  197.* 

Spitzbergen:  coal  fields  of,  428;  coal  re- 
sources of,  409. 

Splint  coal,  87,  88. 

Split,  215.* 

Split-volatile  ratio,  112. 

Spontaneous  combustion,  307;  chemical 
causes  of,  32. 

Spruces,  211. 

Square-chamber  method,  287. 

Squeezes,  214,  215. 

Standardization  of  calorimeter,  77. 

Stansfield,  E.,  32,  326. 

Stanton,  F.  M.,  5,  44,  73. 

Steam  coals,  314. 

Steinkohle,  2 

Stemkoenig,  L.  A.,  38. 

Stephenson,  George,  296. 

Sterling,  Paul,  300. 

Stern,  H.,  307. 

Stevenson,  J.  J.,  124,  128,  129,  138;  illus- 
tration by,  369,  370. 

Stigmaria,  130,  153,  193;  S.  ficoides,  196; 
S.  ficoides,  191.* 

Stink  damp,  295. 

Stock,  H.  H.,  96,  363;  illustration  by 
278,  280,  362. 

Stohman's  solution,  76. 

Stone  coal,  94. 

Stone  damp,  295. 


Stopes,  M.  C.,  230. 

Storage,  306;  deterioration  of  coal  in,  309 

Storrs,  L.  S.,  387. 

Stout,  D.  A.,  237. 

Strahan,  A.,  7,  107,  166,  173,  407;  illus- 
tration by,  224;  and  Pollard,  diagram 
by,  165,  167. 

Streak,  8,  9. 

Streptococcus,  159. 

Strike,  221.* 

Stringer  of  coal,  221.* 

Stripping  Mammoth  seam,  265.* 

Stripping  method,  264. 

Structural  contours,  248. 

Structural  features  of  coal  seams,  214. 

Stumps  in  Coal  Measures,  150.* 

Stur,  D.,  192. 

Subbituminous  coal,  84,  86,  93.* 

Succinite,  103. 

Sullivan  Machine  Co.,  illustration  by,  289. 

Sulphates  in  coal,  34. 

Sulphides  in  coal,  34. 

Sulphur,  33;  determination  of,  by  Eschka 
method,  56;  in  ash,  62;  in  coke,  33, 
316;  inorganic,  34;  organic,  35. 

Sulphur  balls,  34,  230. 

Sulphur  diamonds,  34. 

Sulphuretted  hydrogen,  295. 

Sulphurous  gases,  27. 

Sumatra  Swamp,  138. 

Summit  Hill,  95. 

Superbituminous  coal,  92. 

Sussmilch,  C.  A.,  156,  210. 

Sweden:  coal  fields  of,  428;  coal  resources 
of,  409. 

Swells,  214,  215. 

Swift,  illustration  by,  282. 

Switzerland,  coal  in,  419. 

Syncline:     at    Hazleton,    236;*     pitching, 

222.* 

Synclinorium,  223. 

System  of  Mineralogy,  Dana's  2. 

Taeniopteris  Newberriana,  204.* 

Taff,  J.  A.,  98,  385- 

Tantalus  Mine  on  Yukon  River,  351.* 

Tasmania,  coal  in,  447. 

Tasmanite  shale,  447. 

Tauber's  drying  apparatus,  66. 


INDEX 


461 


Taxaceae,  211. 

Taylor,  C.  A.,  70. 

Temperature,      effect      on      constituents, 

evolved,  26. 
Tennessee,  coal  in,  378. 
Terre  d'ombre,  86 
Texas,  coal  in,  386. 
Thallophytes,  186,  188. 
Theophrastus,  2. 
Thick    seams:     bench   working   in,    288;* 

mining  in,  284. 

Thickening  of  seams  in  anticlines,  223. 
Thickest  seam  in  world,  214. 
Thickness    of    formation:     determination 

of,  245;  curve  for  graphic  determination 

of,  246. 
Theissen,  R.,  9,  n,  13,  14,  15,  20,  34,36, 

101,  130,  176;  illustration  by,  10,  12,  14, 

16,  19,  35- 
Thin  seams:    mined  in  foreign  countries, 

255 ;  mined  in  United  States,  table  of,  254. 
Thin  sections,  preparation  of,  12. 
Thomas,  J.  W.,  23,  24. 
Thracius  lapis,  2. 
Throw,  225. 
Thrust  fault,  225. 
Tile  burning  coals,  313. 
Time  since  burial,  163. 
Topographic    conditions    in    coal-forming 

periods,  150. 
Torbanite,  87,  91. 

Toronto,  Canada,  glacial  deposits,  157. 
" Tortoises"  220. 
Transformation  of  vegetal  matter  to  coal, 

157- 

Transportation  theory,  125. 
Transvaal,  coal  in,  441. 
Tree    trunks    in    Coal    Measures    at    St. 

£tienne,  148,*  152.* 
Trees,  composition  of,  161. 
Trescot,  T.  C.,  68. 

Trinidad,  Colorado,  section  near,  389. 
Trinkerite,  104. 

Tri-radiate  lines  in  spores,  14.* 
Tschernyschew,  Th,  426. 
Tunnel,  266. 

Turbidimeter,  Jackson's  candle,  60. 
Turkey,  coal  in,  425. 
Turn-out,  271. 


Ultimate  analysis,  63. 

Unconformity,  227. 

Underclays,  origin  of,  153. 

Underground  work,  264. 

Uniontown,  Pa.,  Quadrangle,  structure 
section  of,  366. 

United  States:  coal  in,  352;  coal  produc- 
tion of,  352,  353,  354;  distribution  of 
coal  of,  by  kinds,  355;  geological  age 
of  coal  formations  of,  360;  map  of, 
PI.  XII;  table  of  coal  resources  of,  357, 
358,  359- 

Upthrow  side,  of  fault,  226. 

Uses  of  coal,  299. 

Utah:  coal  in,  391;  coal  of,  tested,  28. 

Value  of  world's  production  in  1913,  i. 
Valuation  of  coal  lands,  238,  250. 
Vanadium  in  coal,  39. 
Vandalia,   Ind.,  photomicrograph  of  coal 

from,  19. 

Varieties  of  coal,  82. 
Vascular  cryptogams,  180,  182. 
Venezuela,  coal  in,  404. 
Venice,  Gulf  of,  peat  in,  140. 
Victoria,  coal  in,  445. 
Vignon,  Leo,  30,  88. 

Virginia:  coal  in,  375;  first  mining  in,  i. 
Volatile  constituents,  escape  of,  from  seam, 

169. 
Volatile    matter:     determination    of,    54; 

furnace  for  determination  of,  54.* 
Voltzia,  182. 

Walchia,  182,  213;  W.  frondosa,  210.* 

Wales,  coal  resources  of,  408,  412. 

WaUerius,  J.  G.,  84. 

Walsen  Mine,  natural  coke  of,  99. 

Washington,  coal  in,  396. 

Water  gas,  312. 

Watson,  D.  M.  S.,  230. 

Waxes,  composition  of,  20. 

Wedemeyer,  K.,  68. 

Weight  of  coal  in  foot-acre,  258. 

Welsh  anthracite,  specific  gravity  of,  96. 

Welsh  coals,  tests  on,  24. 

West  Indies,  coal  fields  of,  401. 

West  Virginia,  coal  in,  372. 

Western  Australia,  coal  in,  447. 


462 


INDEX 


Wheeler,  R.  V.,  21,  27,  28,  31,  32. 

Wheelerite,  104. 

Whewellite,  20. 

Whitaker,  M,  C.,  25. 

White,  D.,  ii,  12,  14,  20,  33,  88,  101,  102, 
130,  156,  166,  170,  176,  195,  .196,  203, 
368;  illustration  by,  367. 

White,  I.  C.,  193,  372,  405;  illustration  by, 
367,  368. 

White  damp,  292. 

White's  classification,  in. 

Wieland,  G.  R.,  207;  illustration  by,  208. 

Wilder  F.,  illustration  by,  394. 

Wilkes-Barre,  Pa.,  structure  section  at,  362. 

Willputte  oven,  322. 

Witham,  H.,  n,  126. 

Wood:  changed  to  coal,  164;  composi- 
tion of,  19. 

Woodworth,  J.  B.,  375. 

Worrell,  S.  H.,  386. 


Wright,  C.  L.,  311. 
Wyoming  basin,  Pa.,  171. 
Wyoming,  coal  in,  392. 

Xyloid  lignites,  solubility  of,  29. 
Xyloid  material,  9. 
Xylon,  n. 

Yancey,  H.  J.,  306. 

Yorkshire  jet,  97. 

Yukon  Territory,  coal  in,  350. 

Zalessky,  M.  D.,  176,  235. 

Zamia,  207. 

Zamites,  207. 

Zeiller,  R.,  190,  195,  202,  203,  204,  207; 

illustration  by,  179,  183,  187,  189,  194, 

199,  201,  205,  206. 
Zern,  E.  N.,  315,  363. 


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